diff --git a/config/external/moz.build b/config/external/moz.build
index 89378dafd1..de16793c84 100644
--- a/config/external/moz.build
+++ b/config/external/moz.build
@@ -55,7 +55,7 @@ external_dirs += [
     'media/psshparser'
 ]
 
-if CONFIG['MOZ_LINKER']:
+if CONFIG['MOZ_UPDATER']:
     external_dirs += ['modules/xz-embedded']
 
 DIRS += ['../../' + i for i in external_dirs]
diff --git a/devtools/shared/css/generated/properties-db.js b/devtools/shared/css/generated/properties-db.js
index bb88befb7e..dc4df73b39 100644
--- a/devtools/shared/css/generated/properties-db.js
+++ b/devtools/shared/css/generated/properties-db.js
@@ -2073,6 +2073,7 @@ exports.CSS_PROPERTIES = {
       "-moz-min-content",
       "auto",
       "calc",
+      "content",
       "inherit",
       "initial",
       "unset"
@@ -2095,6 +2096,7 @@ exports.CSS_PROPERTIES = {
       "-moz-min-content",
       "auto",
       "calc",
+      "content",
       "inherit",
       "initial",
       "unset"
@@ -2931,10 +2933,8 @@ exports.CSS_PROPERTIES = {
       "grid-auto-flow",
       "grid-auto-rows",
       "grid-column-end",
-      "grid-column-gap",
       "grid-column-start",
       "grid-row-end",
-      "grid-row-gap",
       "grid-row-start",
       "grid-template-areas",
       "grid-template-columns",
@@ -3029,6 +3029,7 @@ exports.CSS_PROPERTIES = {
       "quotes",
       "resize",
       "right",
+      "row-gap",
       "ruby-align",
       "ruby-position",
       "scroll-behavior",
@@ -3232,6 +3233,7 @@ exports.CSS_PROPERTIES = {
       "column-reverse",
       "condensed",
       "contain",
+      "content",
       "content-box",
       "contents",
       "cover",
@@ -5841,6 +5843,7 @@ exports.CSS_PROPERTIES = {
       "-moz-min-content",
       "auto",
       "calc",
+      "content",
       "inherit",
       "initial",
       "unset"
@@ -5863,6 +5866,7 @@ exports.CSS_PROPERTIES = {
       "-moz-min-content",
       "auto",
       "calc",
+      "content",
       "inherit",
       "initial",
       "unset"
@@ -6328,17 +6332,11 @@ exports.CSS_PROPERTIES = {
       "unset"
     ]
   },
-  "grid": {
+  "gap": {
     "isInherited": false,
     "subproperties": [
-      "grid-template-areas",
-      "grid-template-rows",
-      "grid-template-columns",
-      "grid-auto-flow",
-      "grid-auto-rows",
-      "grid-auto-columns",
-      "grid-row-gap",
-      "grid-column-gap"
+      "row-gap",
+      "column-gap"
     ],
     "supports": [
       6,
@@ -6347,6 +6345,27 @@ exports.CSS_PROPERTIES = {
     "values": [
       "-moz-calc",
       "calc",
+      "inherit",
+      "initial",
+      "normal",
+      "unset"
+    ]
+  },
+  "grid": {
+    "isInherited": false,
+    "subproperties": [
+      "grid-template-areas",
+      "grid-template-rows",
+      "grid-template-columns",
+      "grid-auto-flow",
+      "grid-auto-rows",
+      "grid-auto-columns"
+    ],
+    "supports": [
+      6,
+      8
+    ],
+    "values": [
       "inherit",
       "initial",
       "unset"
@@ -6443,7 +6462,7 @@ exports.CSS_PROPERTIES = {
   "grid-column-gap": {
     "isInherited": false,
     "subproperties": [
-      "grid-column-gap"
+      "column-gap"
     ],
     "supports": [
       6,
@@ -6454,6 +6473,7 @@ exports.CSS_PROPERTIES = {
       "calc",
       "inherit",
       "initial",
+      "normal",
       "unset"
     ]
   },
@@ -6474,8 +6494,8 @@ exports.CSS_PROPERTIES = {
   "grid-gap": {
     "isInherited": false,
     "subproperties": [
-      "grid-row-gap",
-      "grid-column-gap"
+      "row-gap",
+      "column-gap"
     ],
     "supports": [
       6,
@@ -6486,6 +6506,7 @@ exports.CSS_PROPERTIES = {
       "calc",
       "inherit",
       "initial",
+      "normal",
       "unset"
     ]
   },
@@ -6521,7 +6542,7 @@ exports.CSS_PROPERTIES = {
   "grid-row-gap": {
     "isInherited": false,
     "subproperties": [
-      "grid-row-gap"
+      "row-gap"
     ],
     "supports": [
       6,
@@ -6532,6 +6553,7 @@ exports.CSS_PROPERTIES = {
       "calc",
       "inherit",
       "initial",
+      "normal",
       "unset"
     ]
   },
@@ -8335,6 +8357,24 @@ exports.CSS_PROPERTIES = {
       "unset"
     ]
   },
+  "row-gap": {
+    "isInherited": false,
+    "subproperties": [
+      "row-gap"
+    ],
+    "supports": [
+      6,
+      8
+    ],
+    "values": [
+      "-moz-calc",
+      "calc",
+      "inherit",
+      "initial",
+      "normal",
+      "unset"
+    ]
+  },
   "ruby-align": {
     "isInherited": true,
     "subproperties": [
diff --git a/gfx/2d/BaseRect.h b/gfx/2d/BaseRect.h
index 57d01ba09b..b1eed9ddb9 100644
--- a/gfx/2d/BaseRect.h
+++ b/gfx/2d/BaseRect.h
@@ -9,6 +9,7 @@
 #include <algorithm>
 #include <cmath>
 #include <ostream>
+#include <limits>
 
 #include "mozilla/Assertions.h"
 #include "mozilla/FloatingPoint.h"
diff --git a/js/src/builtin/String.js b/js/src/builtin/String.js
index c70f8558be..233a7323b2 100644
--- a/js/src/builtin/String.js
+++ b/js/src/builtin/String.js
@@ -969,12 +969,14 @@ function String_static_trimStart(string) {
         ThrowTypeError(JSMSG_MISSING_FUN_ARG, 0, 'String.trimStart');
     return callFunction(std_String_trimStart, string);
 }
+_SetCanonicalName(String_static_trimStart, "trimStart");
 
 function String_static_trimEnd(string) {
     if (arguments.length < 1)
         ThrowTypeError(JSMSG_MISSING_FUN_ARG, 0, 'String.trimEnd');
     return callFunction(std_String_trimEnd, string);
 }
+_SetCanonicalName(String_static_trimEnd, "trimEnd");
 
 function String_static_toLocaleLowerCase(string) {
     if (arguments.length < 1)
diff --git a/js/src/jit/IonBuilder.cpp b/js/src/jit/IonBuilder.cpp
index 2b7ac6b9ce..dae86fd92a 100644
--- a/js/src/jit/IonBuilder.cpp
+++ b/js/src/jit/IonBuilder.cpp
@@ -8181,12 +8181,14 @@ IonBuilder::maybeMarkEmpty(MDefinition* ins)
     // as having no possible types too. This is to avoid degrading
     // subsequent analysis.
     for (size_t i = 0; i < ins->numOperands(); i++) {
-        if (!ins->emptyResultTypeSet())
+        if (!ins->getOperand(i)->emptyResultTypeSet())
             continue;
 
         TemporaryTypeSet* types = alloc().lifoAlloc()->new_<TemporaryTypeSet>();
-        if (types)
+        if (types) {
             ins->setResultTypeSet(types);
+            return;
+        }
     }
 }
 
diff --git a/layout/base/FrameLayerBuilder.cpp b/layout/base/FrameLayerBuilder.cpp
index d38b17adc4..993572cf3a 100644
--- a/layout/base/FrameLayerBuilder.cpp
+++ b/layout/base/FrameLayerBuilder.cpp
@@ -162,7 +162,12 @@ void
 FrameLayerBuilder::DisplayItemData::AddFrame(nsIFrame* aFrame)
 {
   MOZ_RELEASE_ASSERT(mLayer);
-  mFrameList.AppendElement(aFrame);
+  
+  // Make sure we don't add duplicate frames as we're storing these as vectors.
+  // See UXP Issue #1860
+  if (!mFrameList.Contains(aFrame)) {
+    mFrameList.AppendElement(aFrame);
+  }
 
   nsTArray<DisplayItemData*>* array =
     aFrame->GetProperty(FrameLayerBuilder::LayerManagerDataProperty());
@@ -328,8 +333,7 @@ public:
   void Dump(const char *aPrefix = "") {
     printf_stderr("%sLayerManagerData %p\n", aPrefix, this);
 
-    for (auto iter = mDisplayItems.Iter(); !iter.Done(); iter.Next()) {
-      FrameLayerBuilder::DisplayItemData* data = iter.Get()->GetKey();
+    for (auto& data : mDisplayItems) {
 
       nsAutoCString prefix;
       prefix += aPrefix;
@@ -388,7 +392,7 @@ public:
 #ifdef DEBUG_DISPLAY_ITEM_DATA
   LayerManagerData *mParent;
 #endif
-  nsTHashtable<nsRefPtrHashKey<FrameLayerBuilder::DisplayItemData> > mDisplayItems;
+  std::vector<RefPtr<FrameLayerBuilder::DisplayItemData> > mDisplayItems;
   bool mInvalidateAllLayers;
 };
 
@@ -1971,7 +1975,12 @@ FrameLayerBuilder::RemoveFrameFromLayerManager(const nsIFrame* aFrame,
       }
     }
 
-    data->mParent->mDisplayItems.RemoveEntry(data);
+    auto it = std::find(data->mParent->mDisplayItems.begin(),
+                        data->mParent->mDisplayItems.end(),
+                        data);
+    MOZ_ASSERT(it != data->mParent->mDisplayItems.end());
+    std::iter_swap(it, data->mParent->mDisplayItems.end() - 1);
+    data->mParent->mDisplayItems.pop_back();
   }
 
   arrayCopy.Clear();
@@ -2024,27 +2033,40 @@ FrameLayerBuilder::WillEndTransaction()
   NS_ASSERTION(data, "Must have data!");
 
   // Update all the frames that used to have layers.
-  for (auto iter = data->mDisplayItems.Iter(); !iter.Done(); iter.Next()) {
-    DisplayItemData* data = iter.Get()->GetKey();
-    if (!data->mUsed) {
+  auto iter = data->mDisplayItems.begin();
+  while (iter != data->mDisplayItems.end()) {
+    DisplayItemData* did = iter->get();
+    if (!did->mUsed) {
       // This item was visible, but isn't anymore.
-      PaintedLayer* t = data->mLayer->AsPaintedLayer();
-      if (t && data->mGeometry) {
+      PaintedLayer* t = did->mLayer->AsPaintedLayer();
+      if (t && did->mGeometry) {
 #ifdef MOZ_DUMP_PAINTING
         if (nsLayoutUtils::InvalidationDebuggingIsEnabled()) {
-          printf_stderr("Invalidating unused display item (%i) belonging to frame %p from layer %p\n", data->mDisplayItemKey, data->mFrameList[0], t);
+          printf_stderr("Invalidating unused display item (%i) belonging to frame %p from layer %p\n", did->mDisplayItemKey, did->mFrameList[0], t);
         }
 #endif
         InvalidatePostTransformRegion(t,
-                                      data->mGeometry->ComputeInvalidationRegion(),
-                                      data->mClip,
+                                      did->mGeometry->ComputeInvalidationRegion(),
+                                      did->mClip,
                                       GetLastPaintOffset(t));
       }
 
-      data->ClearAnimationCompositorState();
-      iter.Remove();
+      did->ClearAnimationCompositorState();
+
+      // Remove this item. Swapping it with the last element first is
+      // quicker than erasing from the middle.
+      if (iter != data->mDisplayItems.end() - 1) {
+        std::iter_swap(iter, data->mDisplayItems.end() - 1);
+        data->mDisplayItems.pop_back();
+      } else {
+        data->mDisplayItems.pop_back();
+        break;
+      }
+
+      // Don't increment iter because we still need to process the item which was moved.
     } else {
-      ComputeGeometryChangeForItem(data);
+      ComputeGeometryChangeForItem(did);
+      iter++;
     }
   }
 
@@ -4800,7 +4822,7 @@ FrameLayerBuilder::StoreDataForFrame(nsDisplayItem* aItem, Layer* aLayer, LayerS
 
   data->BeginUpdate(aLayer, aState, mContainerLayerGeneration, aItem);
 
-  lmd->mDisplayItems.PutEntry(data);
+  lmd->mDisplayItems.push_back(data);
   return data;
 }
 
@@ -4824,7 +4846,7 @@ FrameLayerBuilder::StoreDataForFrame(nsIFrame* aFrame,
 
   data->BeginUpdate(aLayer, aState, mContainerLayerGeneration);
 
-  lmd->mDisplayItems.PutEntry(data);
+  lmd->mDisplayItems.push_back(data);
 }
 
 FrameLayerBuilder::ClippedDisplayItem::ClippedDisplayItem(nsDisplayItem* aItem,
@@ -5558,10 +5580,19 @@ FrameLayerBuilder::BuildContainerLayerFor(nsDisplayListBuilder* aBuilder,
       flattenToSingleLayer = true;
 
       // Restore DisplayItemData
-      for (auto iter = data->mDisplayItems.Iter(); !iter.Done(); iter.Next()) {
-        DisplayItemData* data = iter.Get()->GetKey();
-        if (data->mUsed && data->mContainerLayerGeneration >= mContainerLayerGeneration) {
-          iter.Remove();
+      auto iter = data->mDisplayItems.begin();
+      while (iter != data->mDisplayItems.end()) {
+        DisplayItemData* did = iter->get();
+        if (did->mUsed && did->mContainerLayerGeneration >= mContainerLayerGeneration) {
+          if (iter != data->mDisplayItems.end() - 1) {
+            std::iter_swap(iter, data->mDisplayItems.end() - 1);
+            data->mDisplayItems.pop_back();
+          } else {
+            data->mDisplayItems.pop_back();
+            break;
+          }
+        } else {
+          iter++;
         }
       }
 
diff --git a/layout/base/crashtests/1156588.html b/layout/base/crashtests/1156588.html
index ed0098f79a..b48bc3af25 100644
--- a/layout/base/crashtests/1156588.html
+++ b/layout/base/crashtests/1156588.html
@@ -2,9 +2,6 @@
 <html>
 <head>
 <meta charset="UTF-8">
-<!--
-user_pref("layout.css.grid.enabled", true);
--->
 <script>
 
 function boom()
diff --git a/layout/base/crashtests/crashtests.list b/layout/base/crashtests/crashtests.list
index 1a3bf667ba..1c8e2713ac 100644
--- a/layout/base/crashtests/crashtests.list
+++ b/layout/base/crashtests/crashtests.list
@@ -467,7 +467,7 @@ load 1116104.html
 load 1127198-1.html
 load 1140198.html
 load 1143535.html
-pref(layout.css.grid.enabled,true) load 1156588.html
+load 1156588.html
 load 1162813.xul
 load 1163583.html
 load 1234622-1.html
diff --git a/layout/base/nsFrameManager.cpp b/layout/base/nsFrameManager.cpp
index d6a6cb46b5..1dbc87ed95 100644
--- a/layout/base/nsFrameManager.cpp
+++ b/layout/base/nsFrameManager.cpp
@@ -90,16 +90,22 @@ public:
   // Removes all entries from the hash table
   void  Clear();
 
-protected:
-  LinkedList<UndisplayedNode>* GetListFor(nsIContent* aParentContent);
-  LinkedList<UndisplayedNode>* GetOrCreateListFor(nsIContent* aParentContent);
-  void AppendNodeFor(UndisplayedNode* aNode, nsIContent* aParentContent);
   /**
    * Get the applicable parent for the map lookup. This is almost always the
    * provided argument, except if it's a <xbl:children> element, in which case
    * it's the parent of the children element.
+   *
+   * All functions that are entry points into code that handles "parent"
+   * objects (used as the hash table keys) must ensure that the parent objects
+   * that they act on (and pass to other code) have been normalized by calling
+   * this method.
    */
-  nsIContent* GetApplicableParent(nsIContent* aParent);
+  static nsIContent* GetApplicableParent(nsIContent* aParent);
+
+protected:
+  LinkedList<UndisplayedNode>* GetListFor(nsIContent* aParentContent);
+  LinkedList<UndisplayedNode>* GetOrCreateListFor(nsIContent* aParentContent);
+  void AppendNodeFor(UndisplayedNode* aNode, nsIContent* aParentContent);
 };
 
 //----------------------------------------------------------------------
@@ -131,6 +137,20 @@ nsFrameManager::Destroy()
 
 //----------------------------------------------------------------------
 
+/* static */ nsIContent*
+nsFrameManager::ParentForUndisplayedMap(const nsIContent* aContent)
+{
+  MOZ_ASSERT(aContent);
+
+  nsIContent* parent = aContent->GetParentElementCrossingShadowRoot();
+  MOZ_ASSERT(parent || !aContent->GetParent(), "no non-elements");
+
+  // Normalize the parent
+  parent = UndisplayedMap::GetApplicableParent(parent);
+
+  return parent;
+}
+
 /* static */ nsStyleContext*
 nsFrameManager::GetStyleContextInMap(UndisplayedMap* aMap,
                                      const nsIContent* aContent)
@@ -138,8 +158,8 @@ nsFrameManager::GetStyleContextInMap(UndisplayedMap* aMap,
   if (!aContent) {
     return nullptr;
   }
-  nsIContent* parent = aContent->GetParentElementCrossingShadowRoot();
-  MOZ_ASSERT(parent || !aContent->GetParent(), "no non-elements");
+
+  nsIContent* parent = ParentForUndisplayedMap(aContent);
   for (UndisplayedNode* node = aMap->GetFirstNode(parent);
        node; node = node->getNext()) {
     if (node->mContent == aContent)
@@ -178,8 +198,7 @@ nsFrameManager::SetStyleContextInMap(UndisplayedMap* aMap,
   MOZ_ASSERT(!GetStyleContextInMap(aMap, aContent),
              "Already have an entry for aContent");
 
-  nsIContent* parent = aContent->GetParentElementCrossingShadowRoot();
-  MOZ_ASSERT(parent || !aContent->GetParent(), "no non-elements");
+  nsIContent* parent = ParentForUndisplayedMap(aContent);
 #ifdef DEBUG
   nsIPresShell* shell = aStyleContext->PresContext()->PresShell();
   NS_ASSERTION(parent || (shell && shell->GetDocument() &&
@@ -194,9 +213,9 @@ nsFrameManager::SetStyleContextInMap(UndisplayedMap* aMap,
   // mUndisplayedMap and mDisplayContentsMap if the bit isn't present on a node
   // that it's handling.
 
-if (parent) {
-  parent->SetMayHaveChildrenWithLayoutBoxesDisabled();
-}
+  if (parent) {
+    parent->SetMayHaveChildrenWithLayoutBoxesDisabled();
+  }
 
   aMap->AddNodeFor(parent, aContent, aStyleContext);
 }
@@ -223,8 +242,7 @@ nsFrameManager::ChangeStyleContextInMap(UndisplayedMap* aMap,
    printf("ChangeStyleContextInMap(%d): p=%p \n", i++, (void *)aContent);
 #endif
 
-  nsIContent* parent = aContent->GetParentElementCrossingShadowRoot();
-  MOZ_ASSERT(parent || !aContent->GetParent(), "no non-elements");
+  nsIContent* parent = ParentForUndisplayedMap(aContent);
 
   for (UndisplayedNode* node = aMap->GetFirstNode(parent);
        node; node = node->getNext()) {
@@ -249,7 +267,11 @@ nsFrameManager::ClearUndisplayedContentIn(nsIContent* aContent,
   if (!mUndisplayedMap) {
     return;
   }
-  
+
+  // This function is an entry point into UndisplayedMap handling code, so we
+  // must call GetApplicableParent so the parent we pass around is correct.
+  aParentContent = UndisplayedMap::GetApplicableParent(aParentContent);
+
   if (aParentContent && 
       !aParentContent->MayHaveChildrenWithLayoutBoxesDisabled()) {
     MOZ_ASSERT(!mUndisplayedMap->GetFirstNode(aParentContent),
@@ -382,6 +404,10 @@ nsFrameManager::ClearDisplayContentsIn(nsIContent* aContent,
     return;
   }
 
+  // This function is an entry point into UndisplayedMap handling code, so we
+  // must call GetApplicableParent so the parent we pass around is correct.
+  aParentContent = UndisplayedMap::GetApplicableParent(aParentContent);
+
   if (aParentContent &&
       !aParentContent->MayHaveChildrenWithLayoutBoxesDisabled()) {
     MOZ_ASSERT(!mDisplayContentsMap->GetFirstNode(aParentContent),
@@ -684,7 +710,8 @@ nsFrameManagerBase::UndisplayedMap::GetApplicableParent(nsIContent* aParent)
 LinkedList<UndisplayedNode>*
 nsFrameManagerBase::UndisplayedMap::GetListFor(nsIContent* aParent)
 {
-  aParent = GetApplicableParent(aParent);
+  MOZ_ASSERT(aParent == GetApplicableParent(aParent),
+             "The parent that we use as the hash key must have been normalized");
 
   LinkedList<UndisplayedNode>* list;
   if (Get(aParent, &list)) {
@@ -697,7 +724,9 @@ nsFrameManagerBase::UndisplayedMap::GetListFor(nsIContent* aParent)
 LinkedList<UndisplayedNode>*
 nsFrameManagerBase::UndisplayedMap::GetOrCreateListFor(nsIContent* aParent)
 {
-  aParent = GetApplicableParent(aParent);
+  MOZ_ASSERT(aParent == GetApplicableParent(aParent),
+             "The parent that we use as the hash key must have been normalized");
+
   return LookupOrAdd(aParent);
 }
 
diff --git a/layout/base/nsFrameManager.h b/layout/base/nsFrameManager.h
index 7537888605..77484fe3f0 100644
--- a/layout/base/nsFrameManager.h
+++ b/layout/base/nsFrameManager.h
@@ -182,6 +182,8 @@ public:
   void RestoreFrameStateFor(nsIFrame*              aFrame,
                                         nsILayoutHistoryState* aState);
 protected:
+  static nsIContent* ParentForUndisplayedMap(const nsIContent* aContent);
+
   void ClearAllMapsFor(nsIContent* aParentContent);
 
   static nsStyleContext* GetStyleContextInMap(UndisplayedMap* aMap,
diff --git a/layout/base/nsGenConList.cpp b/layout/base/nsGenConList.cpp
index bdb47e1838..fb0733f2e7 100644
--- a/layout/base/nsGenConList.cpp
+++ b/layout/base/nsGenConList.cpp
@@ -19,6 +19,7 @@ nsGenConList::Clear()
     delete node;
   }
   mSize = 0;
+  mLastInserted = nullptr;
 }
 
 bool
@@ -41,6 +42,9 @@ nsGenConList::DestroyNodesFor(nsIFrame* aFrame)
     node = nextNode;
   }
 
+  // Modification of the list invalidates the cached pointer.
+  mLastInserted = nullptr;
+
   return true;
 }
 
@@ -108,6 +112,11 @@ nsGenConList::Insert(nsGenConNode* aNode)
   // Check for append.
   if (mList.isEmpty() || NodeAfter(aNode, mList.getLast())) {
     mList.insertBack(aNode);
+  } else if (mLastInserted && mLastInserted != mList.getLast() &&
+             NodeAfter(aNode, mLastInserted) &&
+             NodeAfter(Next(mLastInserted), aNode)) {
+  // Fast path for inserting many consecutive nodes in one place
+  mLastInserted->setNext(aNode);
   } else {
     // Binary search.
 
@@ -142,6 +151,8 @@ nsGenConList::Insert(nsGenConNode* aNode)
   }
   ++mSize;
 
+  mLastInserted = aNode;
+
   // Set the mapping only if it is the first node of the frame.
   // The DEBUG blocks below are for ensuring the invariant required by
   // nsGenConList::DestroyNodesFor. See comment there.
diff --git a/layout/base/nsGenConList.h b/layout/base/nsGenConList.h
index 55bf6bc32e..58421d4301 100644
--- a/layout/base/nsGenConList.h
+++ b/layout/base/nsGenConList.h
@@ -86,7 +86,7 @@ protected:
   uint32_t mSize;
 
 public:
-  nsGenConList() : mSize(0) {}
+  nsGenConList() : mSize(0), mLastInserted(nullptr) {}
   ~nsGenConList() { Clear(); }
   void Clear();
   static nsGenConNode* Next(nsGenConNode* aNode) {
@@ -127,6 +127,10 @@ private:
 
   // Map from frame to the first nsGenConNode of it in the list.
   nsDataHashtable<nsPtrHashKey<nsIFrame>, nsGenConNode*> mNodes;
+
+  // A weak pointer to the node most recently inserted, used to avoid repeated
+  // list traversals in Insert().
+  nsGenConNode* mLastInserted;
 };
 
 #endif /* nsGenConList_h___ */
diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index ccdc5503f8..ccefbaba57 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -145,7 +145,6 @@ using namespace mozilla::layers;
 using namespace mozilla::layout;
 using namespace mozilla::gfx;
 
-#define GRID_ENABLED_PREF_NAME "layout.css.grid.enabled"
 #define GRID_TEMPLATE_SUBGRID_ENABLED_PREF_NAME "layout.css.grid-template-subgrid-value.enabled"
 #define WEBKIT_PREFIXES_ENABLED_PREF_NAME "layout.css.prefixes.webkit"
 #define DISPLAY_FLOW_ROOT_ENABLED_PREF_NAME "layout.css.display-flow-root.enabled"
@@ -198,51 +197,6 @@ static ContentMap& GetContentMap() {
   return *sContentMap;
 }
 
-// When the pref "layout.css.grid.enabled" changes, this function is invoked
-// to let us update kDisplayKTable, to selectively disable or restore the
-// entries for "grid" and "inline-grid" in that table.
-static void
-GridEnabledPrefChangeCallback(const char* aPrefName, void* aClosure)
-{
-  MOZ_ASSERT(strncmp(aPrefName, GRID_ENABLED_PREF_NAME,
-                     ArrayLength(GRID_ENABLED_PREF_NAME)) == 0,
-             "We only registered this callback for a single pref, so it "
-             "should only be called for that pref");
-
-  static int32_t sIndexOfGridInDisplayTable;
-  static int32_t sIndexOfInlineGridInDisplayTable;
-  static bool sAreGridKeywordIndicesInitialized; // initialized to false
-
-  bool isGridEnabled =
-    Preferences::GetBool(GRID_ENABLED_PREF_NAME, false);
-  if (!sAreGridKeywordIndicesInitialized) {
-    // First run: find the position of "grid" and "inline-grid" in
-    // kDisplayKTable.
-    sIndexOfGridInDisplayTable =
-      nsCSSProps::FindIndexOfKeyword(eCSSKeyword_grid,
-                                     nsCSSProps::kDisplayKTable);
-    MOZ_ASSERT(sIndexOfGridInDisplayTable >= 0,
-               "Couldn't find grid in kDisplayKTable");
-    sIndexOfInlineGridInDisplayTable =
-      nsCSSProps::FindIndexOfKeyword(eCSSKeyword_inline_grid,
-                                     nsCSSProps::kDisplayKTable);
-    MOZ_ASSERT(sIndexOfInlineGridInDisplayTable >= 0,
-               "Couldn't find inline-grid in kDisplayKTable");
-    sAreGridKeywordIndicesInitialized = true;
-  }
-
-  // OK -- now, stomp on or restore the "grid" entries in kDisplayKTable,
-  // depending on whether the grid pref is enabled vs. disabled.
-  if (sIndexOfGridInDisplayTable >= 0) {
-    nsCSSProps::kDisplayKTable[sIndexOfGridInDisplayTable].mKeyword =
-      isGridEnabled ? eCSSKeyword_grid : eCSSKeyword_UNKNOWN;
-  }
-  if (sIndexOfInlineGridInDisplayTable >= 0) {
-    nsCSSProps::kDisplayKTable[sIndexOfInlineGridInDisplayTable].mKeyword =
-      isGridEnabled ? eCSSKeyword_inline_grid : eCSSKeyword_UNKNOWN;
-  }
-}
-
 // When the pref "layout.css.prefixes.webkit" changes, this function is invoked
 // to let us update kDisplayKTable, to selectively disable or restore the
 // entries for "-webkit-box" and "-webkit-inline-box" in that table.
@@ -7575,8 +7529,6 @@ struct PrefCallbacks
   PrefChangedFunc func;
 };
 static const PrefCallbacks kPrefCallbacks[] = {
-  { GRID_ENABLED_PREF_NAME,
-    GridEnabledPrefChangeCallback },
   { WEBKIT_PREFIXES_ENABLED_PREF_NAME,
     WebkitPrefixEnabledPrefChangeCallback },
   { TEXT_ALIGN_UNSAFE_ENABLED_PREF_NAME,
diff --git a/layout/generic/crashtests/1015562.html b/layout/generic/crashtests/1015562.html
index 8975e64f2a..353ae40e35 100644
--- a/layout/generic/crashtests/1015562.html
+++ b/layout/generic/crashtests/1015562.html
@@ -3,10 +3,6 @@
 <head>
 <script>
 
-/*
-user_pref("layout.css.grid.enabled", true);
-*/
-
 function boom()
 {
     document.getElementById("r").appendChild(document.createTextNode("B"));
diff --git a/layout/generic/crashtests/1156257.html b/layout/generic/crashtests/1156257.html
index e58c1ba5db..4799926299 100644
--- a/layout/generic/crashtests/1156257.html
+++ b/layout/generic/crashtests/1156257.html
@@ -2,9 +2,6 @@
 <html>
 <head>
 <meta charset="UTF-8">
-<!--
-user_pref("layout.css.grid.enabled", true);
--->
 <script>
 function boom()
 {
diff --git a/layout/generic/crashtests/crashtests.list b/layout/generic/crashtests/crashtests.list
index 71c8c8f0c9..2fc35c6a70 100644
--- a/layout/generic/crashtests/crashtests.list
+++ b/layout/generic/crashtests/crashtests.list
@@ -566,7 +566,7 @@ load 986899.html
 load 1001233.html
 load 1001258-1.html
 load 1003441.xul
-pref(layout.css.grid.enabled,true) load 1015562.html
+load 1015562.html
 asserts(1-2) load 1015563-1.html
 asserts(1-2) load 1015563-2.html
 asserts(0-300) load 1015844.html # bug 574889
@@ -589,7 +589,7 @@ load 1146107.html
 load 1146114.html
 load 1153695.html
 load 1156222.html
-pref(layout.css.grid.enabled,true) load 1156257.html
+load 1156257.html
 load 1157011.html
 load 1169420-1.html
 load 1169420-2.html
@@ -601,9 +601,9 @@ load 1222783.xhtml
 load 1223568-1.html
 load 1223568-2.html
 load 1224230-1.html
-pref(layout.css.grid.enabled,true) load 1225118.html
-pref(layout.css.grid.enabled,true) load 1225376.html
-pref(layout.css.grid.enabled,true) load 1225592.html
+load 1225118.html
+load 1225376.html
+load 1225592.html
 load 1229437-1.html
 load 1229437-2.html
 pref(dom.details_element.enabled,true) load details-containing-only-text.html
diff --git a/layout/generic/nsColumnSetFrame.cpp b/layout/generic/nsColumnSetFrame.cpp
index 90d425ccf4..99733c549b 100644
--- a/layout/generic/nsColumnSetFrame.cpp
+++ b/layout/generic/nsColumnSetFrame.cpp
@@ -183,15 +183,15 @@ nsColumnSetFrame::GetAvailableContentBSize(const ReflowInput& aReflowInput)
 
 static nscoord
 GetColumnGap(nsColumnSetFrame*    aFrame,
-             const nsStyleColumn* aColStyle,
              nscoord              aPercentageBasis)
 {
-  const auto& columnGap = aColStyle->mColumnGap;
-  if (columnGap.GetUnit() == eStyleUnit_Normal) {
+  const nsStylePosition* positionData = aFrame->StylePosition();
+  if (positionData->mColumnGap.GetUnit() == eStyleUnit_Normal) {
     return aFrame->StyleFont()->mFont.size;
   }
 
-  return nsLayoutUtils::ResolveGapToLength(columnGap, aPercentageBasis);
+  return nsLayoutUtils::ResolveGapToLength(positionData->mColumnGap,
+                                           aPercentageBasis);
 }
 
 nsColumnSetFrame::ReflowConfig
@@ -224,7 +224,7 @@ nsColumnSetFrame::ChooseColumnStrategy(const ReflowInput& aReflowInput,
     colBSize = std::min(colBSize, aReflowInput.ComputedMaxBSize());
   }
 
-  nscoord colGap = GetColumnGap(this, colStyle, aReflowInput.ComputedISize());
+  nscoord colGap = GetColumnGap(this, aReflowInput.ComputedISize());
   int32_t numColumns = colStyle->mColumnCount;
 
   // If column-fill is set to 'balance', then we want to balance the columns.
@@ -400,7 +400,7 @@ nsColumnSetFrame::GetMinISize(nsRenderingContext *aRenderingContext)
     // include n-1 column gaps.
     colISize = iSize;
     iSize *= colStyle->mColumnCount;
-    nscoord colGap = GetColumnGap(this, colStyle, NS_UNCONSTRAINEDSIZE);
+    nscoord colGap = GetColumnGap(this, NS_UNCONSTRAINEDSIZE);
     iSize += colGap * (colStyle->mColumnCount - 1);
     // The multiplication above can make 'width' negative (integer overflow),
     // so use std::max to protect against that.
@@ -421,7 +421,7 @@ nsColumnSetFrame::GetPrefISize(nsRenderingContext *aRenderingContext)
   nscoord result = 0;
   DISPLAY_PREF_WIDTH(this, result);
   const nsStyleColumn* colStyle = StyleColumn();
-  nscoord colGap = GetColumnGap(this, colStyle, NS_UNCONSTRAINEDSIZE);
+  nscoord colGap = GetColumnGap(this, NS_UNCONSTRAINEDSIZE);
 
   nscoord colISize;
   if (colStyle->mColumnWidth.GetUnit() == eStyleUnit_Coord) {
diff --git a/layout/generic/nsContainerFrame.cpp b/layout/generic/nsContainerFrame.cpp
index 47afed9de1..aa33c97b2c 100644
--- a/layout/generic/nsContainerFrame.cpp
+++ b/layout/generic/nsContainerFrame.cpp
@@ -947,8 +947,29 @@ nsContainerFrame::ComputeAutoSize(nsRenderingContext* aRenderingContext,
                        aBorder.ISize(aWM) - aPadding.ISize(aWM);
   // replaced elements always shrink-wrap
   if ((aFlags & ComputeSizeFlags::eShrinkWrap) || IsFrameOfType(eReplaced)) {
-    // don't bother setting it if the result won't be used
-    if (StylePosition()->ISize(aWM).GetUnit() == eStyleUnit_Auto) {
+    const nsStylePosition* position = StylePosition();
+
+    bool isFlexBasisContent = false;
+    if (IsFlexItem()) {
+      uint32_t flexDirection =
+        GetParent()->StylePosition()->mFlexDirection;
+      bool isInlineFlexItem =
+        flexDirection == NS_STYLE_FLEX_DIRECTION_ROW ||
+        flexDirection == NS_STYLE_FLEX_DIRECTION_ROW_REVERSE;
+      isFlexBasisContent =
+        position->mFlexBasis.GetUnit() == eStyleUnit_Enumerated &&
+        position->mFlexBasis.GetIntValue() == NS_STYLE_FLEX_BASIS_CONTENT &&
+        isInlineFlexItem;
+    }
+
+    // Only bother computing our 'auto' ISize if the result will be used.
+    // It'll be used under two scenarios:
+    // - If our ISize property is itself 'auto'.
+    // - If we're using flex-basis in place of our ISize property (i.e. we're a
+    // flex item with our inline axis being the main axis), AND we have
+    // flex-basis:content.
+    bool isAuto = position->ISize(aWM).GetUnit() == eStyleUnit_Auto;
+    if (isAuto || isFlexBasisContent) {
       result.ISize(aWM) = ShrinkWidthToFit(aRenderingContext, availBased, aFlags);
     }
   } else {
diff --git a/layout/generic/nsFlexContainerFrame.cpp b/layout/generic/nsFlexContainerFrame.cpp
index 8a393c3fe7..4429111e46 100644
--- a/layout/generic/nsFlexContainerFrame.cpp
+++ b/layout/generic/nsFlexContainerFrame.cpp
@@ -34,6 +34,7 @@ typedef nsFlexContainerFrame::FlexboxAxisTracker FlexboxAxisTracker;
 typedef nsFlexContainerFrame::StrutInfo StrutInfo;
 typedef nsFlexContainerFrame::CachedMeasuringReflowResult
           CachedMeasuringReflowResult;
+typedef nsLayoutUtils::IntrinsicISizeType IntrinsicISizeType;
 
 static mozilla::LazyLogModule gFlexContainerLog("nsFlexContainerFrame");
 
@@ -811,17 +812,23 @@ protected:
 class nsFlexContainerFrame::FlexLine : public LinkedListElement<FlexLine>
 {
 public:
-  FlexLine()
+  explicit FlexLine(nscoord aMainGapSize)
   : mNumItems(0),
     mNumFrozenItems(0),
     mTotalInnerHypotheticalMainSize(0),
     mTotalOuterHypotheticalMainSize(0),
     mLineCrossSize(0),
     mFirstBaselineOffset(nscoord_MIN),
-    mLastBaselineOffset(nscoord_MIN)
+    mLastBaselineOffset(nscoord_MIN),
+    mMainGapSize(aMainGapSize)
   {}
 
-  // Returns the sum of our FlexItems' outer hypothetical main sizes.
+  nscoord GetSumOfGaps() const {
+    return mNumItems > 0 ? (mNumItems - 1) * mMainGapSize : 0;
+  }
+
+  // Returns the sum of our FlexItems' outer hypothetical main sizes
+  // and the sum of the main axis {row,column}-gaps between items.
   // ("outer" = margin-box, and "hypothetical" = before flexing)
   nscoord GetTotalOuterHypotheticalMainSize() const {
     return mTotalOuterHypotheticalMainSize;
@@ -890,8 +897,16 @@ public:
     if (aItem->IsFrozen()) {
       mNumFrozenItems++;
     }
-    mTotalInnerHypotheticalMainSize += aItemInnerHypotheticalMainSize;
+
+    mTotalInnerHypotheticalMainSize += (aItemOuterHypotheticalMainSize -
+                                        aItemInnerHypotheticalMainSize);
     mTotalOuterHypotheticalMainSize += aItemOuterHypotheticalMainSize;
+
+    // If the item added was not the first item in the line, we add in
+    // any gap space as needed.
+    if (mNumItems >= 2) {
+        mTotalOuterHypotheticalMainSize += mMainGapSize;
+    }
   }
 
   // Computes the cross-size and baseline position of this FlexLine, based on
@@ -935,6 +950,22 @@ public:
     return mLastBaselineOffset;
   }
 
+  /**
+   * Returns the number of items held in this line. Used for total gap
+   * calculations.
+   */
+  uint32_t GetNumItems() const {
+    return mNumItems;
+  }
+
+  /**
+   * Returns the gap size in the main axis for this line. Used for gap
+   * calculations.
+   */
+  nscoord GetMainGapSize() const {
+    return mMainGapSize;
+  }
+
   // Runs the "Resolving Flexible Lengths" algorithm from section 9.7 of the
   // CSS flexbox spec to distribute aFlexContainerMainSize among our flex items.
   void ResolveFlexibleLengths(nscoord aFlexContainerMainSize);
@@ -973,6 +1004,9 @@ private:
   nscoord mLineCrossSize;
   nscoord mFirstBaselineOffset;
   nscoord mLastBaselineOffset;
+
+  // Maintain size of each {row,column}-gap in the main axis
+  const nscoord mMainGapSize;
 };
 
 // Information about a strut left behind by a FlexItem that's been collapsed
@@ -2241,6 +2275,9 @@ public:
                "miscounted the number of auto margins");
   }
 
+  // Advances past the gap space (if any) between two flex items
+  void TraverseGap(nscoord aGapSize) { mPosition += aGapSize; }
+
   // Advances past the packing space (if any) between two flex items
   void TraversePackingSpace();
 
@@ -2266,7 +2303,11 @@ public:
                            const ReflowInput& aReflowInput,
                            nscoord aContentBoxCrossSize,
                            bool aIsCrossSizeDefinite,
-                           const FlexboxAxisTracker& aAxisTracker);
+                           const FlexboxAxisTracker& aAxisTracker,
+                           const nscoord aCrossGapSize);
+
+  // Advances past the gap (if any) between two flex lines
+  void TraverseGap() { mPosition += mCrossGapSize; }
 
   // Advances past the packing space (if any) between two flex lines
   void TraversePackingSpace();
@@ -2288,6 +2329,8 @@ private:
   uint32_t mNumPackingSpacesRemaining;
   // XXX this should be uint16_t when we add explicit fallback handling
   uint8_t  mAlignContent;
+
+  const nscoord mCrossGapSize;
 };
 
 // Utility class for managing our position along the cross axis, *within* a
@@ -2581,14 +2624,12 @@ FlexLine::ResolveFlexibleLengths(nscoord aFlexContainerMainSize)
   }
   MOZ_ASSERT(!IsEmpty(), "empty lines should take the early-return above");
 
-  // Subtract space occupied by our items' margins/borders/padding, so we can
-  // just be dealing with the space available for our flex items' content
-  // boxes.
-  nscoord spaceReservedForMarginBorderPadding =
-    mTotalOuterHypotheticalMainSize - mTotalInnerHypotheticalMainSize;
-
+  // Subtract space occupied by our items' margins/borders/padding/gaps, so
+  // we can just be dealing with the space available for our flex items'
+  // content boxes.
   nscoord spaceAvailableForFlexItemsContentBoxes =
-    aFlexContainerMainSize - spaceReservedForMarginBorderPadding;
+    aFlexContainerMainSize - (mTotalInnerHypotheticalMainSize +
+                              GetSumOfGaps());
 
   nscoord origAvailableFreeSpace;
   bool isOrigAvailFreeSpaceInitialized = false;
@@ -2867,6 +2908,9 @@ MainAxisPositionTracker::
     mNumAutoMarginsInMainAxis += item->GetNumAutoMarginsInAxis(mAxis);
   }
 
+  // Subtract space required for row/col gap from the remaining packing space
+  mPackingSpaceRemaining -= aLine->GetSumOfGaps();
+
   if (mPackingSpaceRemaining <= 0) {
     // No available packing space to use for resolving auto margins.
     mNumAutoMarginsInMainAxis = 0;
@@ -3014,12 +3058,14 @@ CrossAxisPositionTracker::
                            const ReflowInput& aReflowInput,
                            nscoord aContentBoxCrossSize,
                            bool aIsCrossSizeDefinite,
-                           const FlexboxAxisTracker& aAxisTracker)
+                           const FlexboxAxisTracker& aAxisTracker,
+                           const nscoord aCrossGapSize)
   : PositionTracker(aAxisTracker.GetCrossAxis(),
                     aAxisTracker.IsCrossAxisReversed()),
     mPackingSpaceRemaining(0),
     mNumPackingSpacesRemaining(0),
-    mAlignContent(aReflowInput.mStylePosition->mAlignContent)
+    mAlignContent(aReflowInput.mStylePosition->mAlignContent),
+    mCrossGapSize(aCrossGapSize)
 {
   MOZ_ASSERT(aFirstLine, "null first line pointer");
 
@@ -3072,6 +3118,11 @@ CrossAxisPositionTracker::
     numLines++;
   }
 
+  // Subtract space required for row/col gap from the remaining packing space
+  MOZ_ASSERT(numLines >= 1,
+             "GenerateFlexLines should've produced at least 1 line");
+  mPackingSpaceRemaining -= aCrossGapSize * (numLines - 1);
+
   // If packing space is negative, 'space-between' and 'stretch' behave like
   // 'flex-start', and 'space-around' and 'space-evenly' behave like 'center'.
   // In those cases, it's simplest to just pretend we have a different
@@ -3673,9 +3724,10 @@ FlexboxAxisTracker::InitAxesFromModernProps(
 // back depending on aShouldInsertAtFront), and returns a pointer to it.
 static FlexLine*
 AddNewFlexLineToList(LinkedList<FlexLine>& aLines,
-                     bool aShouldInsertAtFront)
+                     bool aShouldInsertAtFront,
+                     nscoord aMainGapSize)
 {
-  FlexLine* newLine = new FlexLine();
+  FlexLine* newLine = new FlexLine(aMainGapSize);
   if (aShouldInsertAtFront) {
     aLines.insertFront(newLine);
   } else {
@@ -3692,6 +3744,7 @@ nsFlexContainerFrame::GenerateFlexLines(
   nscoord aAvailableBSizeForContent,
   const nsTArray<StrutInfo>& aStruts,
   const FlexboxAxisTracker& aAxisTracker,
+  nscoord aMainGapSize,
   nsTArray<nsIFrame*>& aPlaceholders, /* out */
   LinkedList<FlexLine>& aLines /* out */)
 {
@@ -3710,7 +3763,8 @@ nsFlexContainerFrame::GenerateFlexLines(
 
   // We have at least one FlexLine. Even an empty flex container has a single
   // (empty) flex line.
-  FlexLine* curLine = AddNewFlexLineToList(aLines, shouldInsertAtFront);
+  FlexLine* curLine = AddNewFlexLineToList(aLines, shouldInsertAtFront,
+                                           aMainGapSize);
 
   nscoord wrapThreshold;
   if (isSingleLine) {
@@ -3759,7 +3813,8 @@ nsFlexContainerFrame::GenerateFlexLines(
     // Honor "page-break-before", if we're multi-line and this line isn't empty:
     if (!isSingleLine && !curLine->IsEmpty() &&
         childFrame->StyleDisplay()->mBreakBefore) {
-      curLine = AddNewFlexLineToList(aLines, shouldInsertAtFront);
+      curLine = AddNewFlexLineToList(aLines, shouldInsertAtFront,
+                                     aMainGapSize);
     }
 
     UniquePtr<FlexItem> item;
@@ -3782,11 +3837,16 @@ nsFlexContainerFrame::GenerateFlexLines(
     // Check if we need to wrap |item| to a new line
     // (i.e. check if its outer hypothetical main size pushes our line over
     // the threshold)
-    if (wrapThreshold != NS_UNCONSTRAINEDSIZE &&
-        !curLine->IsEmpty() && // No need to wrap at start of a line.
-        wrapThreshold < (curLine->GetTotalOuterHypotheticalMainSize() +
-                         itemOuterHypotheticalMainSize)) {
-      curLine = AddNewFlexLineToList(aLines, shouldInsertAtFront);
+    // Don't wrap if unconstrained and if this will be line's first item.
+    if (wrapThreshold != NS_UNCONSTRAINEDSIZE && !curLine->IsEmpty()) {
+      nscoord newOuterSize = curLine->GetTotalOuterHypotheticalMainSize() +
+                             itemOuterHypotheticalMainSize;
+      // Account for gap between this line's previous item and this item
+      newOuterSize += aMainGapSize;
+      if (newOuterSize == nscoord_MAX || newOuterSize > wrapThreshold) {
+        curLine = AddNewFlexLineToList(aLines, shouldInsertAtFront,
+                                       aMainGapSize);
+      }
     }
 
     // Add item to current flex line (and update the line's bookkeeping about
@@ -3798,7 +3858,8 @@ nsFlexContainerFrame::GenerateFlexLines(
     // Honor "page-break-after", if we're multi-line and have more children:
     if (!isSingleLine && childFrame->GetNextSibling() &&
         childFrame->StyleDisplay()->mBreakAfter) {
-      curLine = AddNewFlexLineToList(aLines, shouldInsertAtFront);
+      curLine = AddNewFlexLineToList(aLines, shouldInsertAtFront,
+                                     aMainGapSize);
     }
     itemIdxInContainer++;
   }
@@ -3990,6 +4051,9 @@ FlexLine::PositionItemsInMainAxis(uint8_t aJustifyContent,
     mainAxisPosnTracker.ExitChildFrame(itemMainBorderBoxSize);
     mainAxisPosnTracker.ExitMargin(item->GetMargin());
     mainAxisPosnTracker.TraversePackingSpace();
+    if (item->getNext()) {
+      mainAxisPosnTracker.TraverseGap(mMainGapSize);
+    }
   }
 }
 
@@ -4178,16 +4242,37 @@ nsFlexContainerFrame::Reflow(nsPresContext* aPresContext,
   nscoord contentBoxMainSize = GetMainSizeFromReflowInput(aReflowInput,
                                                           axisTracker);
 
+  // Calculate gap size for main and cross axis
+  nscoord mainGapSize;
+  nscoord crossGapSize;
+  if (axisTracker.IsRowOriented()) {
+    mainGapSize = nsLayoutUtils::ResolveGapToLength(stylePos->mColumnGap,
+                                                    contentBoxMainSize);
+    crossGapSize =
+      nsLayoutUtils::ResolveGapToLength(stylePos->mRowGap,
+                                        GetEffectiveComputedBSize(aReflowInput));
+  } else {
+    mainGapSize = nsLayoutUtils::ResolveGapToLength(stylePos->mRowGap,
+                                                    contentBoxMainSize);
+    NS_WARNING_ASSERTION(aReflowInput.ComputedISize() != NS_UNCONSTRAINEDSIZE,
+                         "Unconstrained inline size; this should only result "
+                         "from huge sizes (not intrinsic sizing w/ orthogonal "
+                         "flows)");
+    crossGapSize =
+      nsLayoutUtils::ResolveGapToLength(stylePos->mColumnGap,
+                                        aReflowInput.ComputedISize());
+  }
+
   AutoTArray<StrutInfo, 1> struts;
   DoFlexLayout(aPresContext, aDesiredSize, aReflowInput, aStatus,
                contentBoxMainSize, availableBSizeForContent,
-               struts, axisTracker);
+               struts, axisTracker, mainGapSize, crossGapSize);
 
   if (!struts.IsEmpty()) {
     // We're restarting flex layout, with new knowledge of collapsed items.
     DoFlexLayout(aPresContext, aDesiredSize, aReflowInput, aStatus,
                  contentBoxMainSize, availableBSizeForContent,
-                 struts, axisTracker);
+                 struts, axisTracker, mainGapSize, crossGapSize);
   }
 }
 
@@ -4312,7 +4397,9 @@ nsFlexContainerFrame::DoFlexLayout(nsPresContext*           aPresContext,
                                    nscoord aContentBoxMainSize,
                                    nscoord aAvailableBSizeForContent,
                                    nsTArray<StrutInfo>& aStruts,
-                                   const FlexboxAxisTracker& aAxisTracker)
+                                   const FlexboxAxisTracker& aAxisTracker,
+                                   nscoord aMainGapSize,
+                                   nscoord aCrossGapSize)
 {
   aStatus = NS_FRAME_COMPLETE;
 
@@ -4324,6 +4411,7 @@ nsFlexContainerFrame::DoFlexLayout(nsPresContext*           aPresContext,
                     aContentBoxMainSize,
                     aAvailableBSizeForContent,
                     aStruts, aAxisTracker,
+                    aMainGapSize,
                     placeholderKids, lines);
 
   if (lines.getFirst()->IsEmpty() &&
@@ -4385,6 +4473,11 @@ nsFlexContainerFrame::DoFlexLayout(nsPresContext*           aPresContext,
     // Now that we've finished with this line's items, size the line itself:
     line->ComputeCrossSizeAndBaseline(aAxisTracker);
     sumLineCrossSizes += line->GetLineCrossSize();
+
+    // Add the cross axis gap space if this is not the last line
+    if (line->getNext()) {
+      sumLineCrossSizes += aCrossGapSize;
+    }
   }
 
   bool isCrossSizeDefinite;
@@ -4397,7 +4490,8 @@ nsFlexContainerFrame::DoFlexLayout(nsPresContext*           aPresContext,
   CrossAxisPositionTracker
     crossAxisPosnTracker(lines.getFirst(),
                          aReflowInput, contentBoxCrossSize,
-                         isCrossSizeDefinite, aAxisTracker);
+                         isCrossSizeDefinite, aAxisTracker,
+                         aCrossGapSize);
 
   // Now that we know the cross size of each line (including
   // "align-content:stretch" adjustments, from the CrossAxisPositionTracker
@@ -4447,6 +4541,10 @@ nsFlexContainerFrame::DoFlexLayout(nsPresContext*           aPresContext,
                                    aAxisTracker);
     crossAxisPosnTracker.TraverseLine(*line);
     crossAxisPosnTracker.TraversePackingSpace();
+
+    if (line->getNext()) {
+      crossAxisPosnTracker.TraverseGap();
+    }
   }
 
   // If the container should derive its baseline from the last FlexLine,
@@ -4817,33 +4915,70 @@ nsFlexContainerFrame::ReflowPlaceholders(nsPresContext* aPresContext,
   }
 }
 
+nscoord
+nsFlexContainerFrame::GetIntrinsicISize(nsRenderingContext* aRenderingContext,
+                                        IntrinsicISizeType aType)
+{
+  nscoord containerISize = 0;
+  RenumberList();
+
+  const nsStylePosition* stylePos = StylePosition();
+  const FlexboxAxisTracker axisTracker(this, GetWritingMode());
+
+  nscoord mainGapSize;
+  if (axisTracker.IsRowOriented()) {
+    mainGapSize = nsLayoutUtils::ResolveGapToLength(stylePos->mColumnGap,
+                                                    NS_UNCONSTRAINEDSIZE);
+  } else {
+    mainGapSize = nsLayoutUtils::ResolveGapToLength(stylePos->mRowGap,
+                                                    NS_UNCONSTRAINEDSIZE);
+  }
+
+  // The loop below sets aside space for a gap before each item besides the
+  // first. This bool helps us handle that special-case.
+  bool onFirstChild = true;
+
+  for (nsIFrame* childFrame : mFrames) {
+    // Skip out-of-flow children because they don't participate in flex layout.
+    if (childFrame->GetType() == nsGkAtoms::placeholderFrame) {
+      continue;
+    }
+
+    nscoord childISize = nsLayoutUtils::IntrinsicForContainer(
+        aRenderingContext, childFrame, aType);
+    // * For a row-oriented single-line flex container, the intrinsic
+    // {min/pref}-isize is the sum of its items' {min/pref}-isizes and
+    // (n-1) column gaps.
+    // * For a column-oriented flex container, the intrinsic min isize
+    // is the max of its items' min isizes.
+    // * For a row-oriented multi-line flex container, the intrinsic
+    // pref isize is former (sum), and its min isize is the latter (max).
+    bool isSingleLine = (NS_STYLE_FLEX_WRAP_NOWRAP == stylePos->mFlexWrap);
+    if (axisTracker.IsRowOriented() &&
+        (isSingleLine || aType == nsLayoutUtils::PREF_ISIZE)) {
+      containerISize += childISize;
+      if (!onFirstChild) {
+        containerISize += mainGapSize;
+      }
+      onFirstChild = false;
+    } else {
+      // col-oriented, or MIN_ISIZE for multi-line row flex container
+      containerISize = std::max(containerISize, childISize);
+    }
+  }
+
+  return containerISize;
+}
+
 /* virtual */ nscoord
 nsFlexContainerFrame::GetMinISize(nsRenderingContext* aRenderingContext)
 {
   nscoord minISize = 0;
   DISPLAY_MIN_WIDTH(this, minISize);
 
-  RenumberList();
+  // TODO: See bug 1454822
+  minISize = GetIntrinsicISize(aRenderingContext, nsLayoutUtils::MIN_ISIZE);
 
-  const nsStylePosition* stylePos = StylePosition();
-  const FlexboxAxisTracker axisTracker(this, GetWritingMode());
-
-  for (nsIFrame* childFrame : mFrames) {
-    nscoord childMinISize =
-      nsLayoutUtils::IntrinsicForContainer(aRenderingContext, childFrame,
-                                           nsLayoutUtils::MIN_ISIZE);
-    // For a horizontal single-line flex container, the intrinsic min
-    // isize is the sum of its items' min isizes.
-    // For a column-oriented flex container, or for a multi-line row-
-    // oriented flex container, the intrinsic min isize is the max of
-    // its items' min isizes.
-    if (axisTracker.IsRowOriented() &&
-        NS_STYLE_FLEX_WRAP_NOWRAP == stylePos->mFlexWrap) {
-      minISize += childMinISize;
-    } else {
-      minISize = std::max(minISize, childMinISize);
-    }
-  }
   return minISize;
 }
 
@@ -4853,24 +4988,8 @@ nsFlexContainerFrame::GetPrefISize(nsRenderingContext* aRenderingContext)
   nscoord prefISize = 0;
   DISPLAY_PREF_WIDTH(this, prefISize);
 
-  RenumberList();
+  // TODO: See bug 1454822
+  prefISize = GetIntrinsicISize(aRenderingContext, nsLayoutUtils::PREF_ISIZE);
 
-  // XXXdholbert Optimization: We could cache our intrinsic widths like
-  // nsBlockFrame does (and return it early from this function if it's set).
-  // Whenever anything happens that might change it, set it to
-  // NS_INTRINSIC_WIDTH_UNKNOWN (like nsBlockFrame::MarkIntrinsicISizesDirty
-  // does)
-  const FlexboxAxisTracker axisTracker(this, GetWritingMode());
-
-  for (nsIFrame* childFrame : mFrames) {
-    nscoord childPrefISize =
-      nsLayoutUtils::IntrinsicForContainer(aRenderingContext, childFrame,
-                                           nsLayoutUtils::PREF_ISIZE);
-    if (axisTracker.IsRowOriented()) {
-      prefISize += childPrefISize;
-    } else {
-      prefISize = std::max(prefISize, childPrefISize);
-    }
-  }
   return prefISize;
 }
diff --git a/layout/generic/nsFlexContainerFrame.h b/layout/generic/nsFlexContainerFrame.h
index 9edcb87974..39de79b577 100644
--- a/layout/generic/nsFlexContainerFrame.h
+++ b/layout/generic/nsFlexContainerFrame.h
@@ -72,6 +72,9 @@ public:
                       const ReflowInput& aReflowInput,
                       nsReflowStatus&          aStatus) override;
 
+  nscoord GetIntrinsicISize(nsRenderingContext* aRenderingContext,
+                            nsLayoutUtils::IntrinsicISizeType aType);
+
   virtual nscoord
     GetMinISize(nsRenderingContext* aRenderingContext) override;
   virtual nscoord
@@ -160,7 +163,9 @@ protected:
                     nscoord aContentBoxMainSize,
                     nscoord aAvailableBSizeForContent,
                     nsTArray<StrutInfo>& aStruts,
-                    const FlexboxAxisTracker& aAxisTracker);
+                    const FlexboxAxisTracker& aAxisTracker,
+                    nscoord aMainGapSize,
+                    nscoord aCrossGapSize);
 
   /**
    * Checks whether our child-frame list "mFrames" is sorted, using the given
@@ -244,6 +249,7 @@ protected:
                          nscoord aAvailableBSizeForContent,
                          const nsTArray<StrutInfo>& aStruts,
                          const FlexboxAxisTracker& aAxisTracker,
+                         nscoord aMainGapSize,
                          nsTArray<nsIFrame*>& aPlaceholders,
                          mozilla::LinkedList<FlexLine>& aLines);
 
diff --git a/layout/generic/nsFrame.cpp b/layout/generic/nsFrame.cpp
index b8e66ecbcd..60f3515c31 100644
--- a/layout/generic/nsFrame.cpp
+++ b/layout/generic/nsFrame.cpp
@@ -4635,6 +4635,61 @@ nsFrame::GetIntrinsicRatio()
   return AspectRatio();
 }
 
+void
+nsFrame::SetCoordToFlexBasis(bool aIsInlineFlexItem,
+                             bool aIntrinsic,
+                             const nsStyleCoord* aFlexBasis,
+                             const nsStyleCoord** aInlineStyle,
+                             const nsStyleCoord** aBlockStyle)
+{
+  auto mainAxisCoord = aIsInlineFlexItem ?
+                       aInlineStyle :
+                       aBlockStyle;
+  // NOTE: If we're a table-wrapper frame, we skip this clause and just stick
+  // with 'main-size:auto' behavior (which -- unlike 'content'
+  // i.e. 'max-content' -- will give us the ability to honor percent sizes on
+  // our table-box child when resolving the flex base size). The flexbox spec
+  // doesn't call for this special case, but webcompat & regression-avoidance
+  // seems to require it, for the time being... Tables sure are special.
+  bool isTableWrapperFrame = GetType() == nsGkAtoms::tableWrapperFrame;
+  // We have a used flex-basis of 'content' if flex-basis explicitly has that
+  // value, OR if flex-basis is 'auto' (deferring to the main-size property)
+  // and the main-size property is also 'auto'.
+  // See https://drafts.csswg.org/css-flexbox-1/#valdef-flex-basis-auto
+  if ((aFlexBasis->GetUnit() == eStyleUnit_Enumerated &&
+       aFlexBasis->GetIntValue() == NS_STYLE_FLEX_BASIS_CONTENT) ||
+      (aFlexBasis->GetUnit() == eStyleUnit_Auto &&
+       (*mainAxisCoord)->GetUnit() == eStyleUnit_Auto)) {
+    // If we get here, we're resolving the flex base size for a flex item,
+    // and we fall into the flexbox spec section 9.2 step 3, substep C (if
+    // we have a definite cross size) or E (if not). And specifically:
+    //
+    // * If we have a definite cross size, we're supposed to resolve our
+    //   main-size based on that and our intrinsic ratio.
+    // * Otherwise, we're supposed to produce our max-content size.
+    //
+    // Conveniently, we can handle both of those scenarios (regardless of
+    // which substep we fall into) by using the 'auto' keyword for our
+    // main-axis coordinate here. (This makes sense, because the spec is
+    // effectively trying to produce the 'auto' sizing behavior).
+    if (aIntrinsic || MOZ_LIKELY(isTableWrapperFrame)) {
+      static const nsStyleCoord autoStyleCoord(eStyleUnit_Auto);
+      *mainAxisCoord = &autoStyleCoord;
+    } else {
+      // (Note: if our main axis is the block axis, then this 'max-content'
+      // value will be treated like 'auto', via the IsAutoBSize() call below.)
+      static const nsStyleCoord maxContStyleCoord(NS_STYLE_WIDTH_MAX_CONTENT,
+                                                  eStyleUnit_Enumerated);
+      *mainAxisCoord = &maxContStyleCoord;
+    }
+  } else if (aFlexBasis->GetUnit() != eStyleUnit_Auto) {
+    // For all other non-'auto' flex-basis values, we just swap in the
+    // flex-basis itself for the main-size property.
+    *mainAxisCoord = aFlexBasis;
+  } // else: flex-basis is 'auto', which is deferring to some explicit
+    // value in mainAxisCoord. So we proceed w/o touching mainAxisCoord.
+}
+
 /* virtual */
 LogicalSize
 nsFrame::ComputeSize(nsRenderingContext* aRenderingContext,
@@ -4689,35 +4744,14 @@ nsFrame::ComputeSize(nsRenderingContext* aRenderingContext,
                      !(GetStateBits() & NS_FRAME_OUT_OF_FLOW));
   bool isInlineFlexItem = false;
   if (isFlexItem) {
-    // Flex items use their "flex-basis" property in place of their main-size
-    // property (e.g. "width") for sizing purposes, *unless* they have
-    // "flex-basis:auto", in which case they use their main-size property after
-    // all.
     uint32_t flexDirection = GetParent()->StylePosition()->mFlexDirection;
     isInlineFlexItem =
       flexDirection == NS_STYLE_FLEX_DIRECTION_ROW ||
       flexDirection == NS_STYLE_FLEX_DIRECTION_ROW_REVERSE;
 
-    // NOTE: The logic here should match the similar chunk for determining
-    // inlineStyleCoord and blockStyleCoord in
-    // nsFrame::ComputeSizeWithIntrinsicDimensions().
     const nsStyleCoord* flexBasis = &(stylePos->mFlexBasis);
-    if (flexBasis->GetUnit() != eStyleUnit_Auto) {
-      if (isInlineFlexItem) {
-        inlineStyleCoord = flexBasis;
-      } else {
-        // One caveat for vertical flex items: We don't support enumerated
-        // values (e.g. "max-content") for height properties yet. So, if our
-        // computed flex-basis is an enumerated value, we'll just behave as if
-        // it were "auto", which means "use the main-size property after all"
-        // (which is "height", in this case).
-        // NOTE: Once we support intrinsic sizing keywords for "height",
-        // we should remove this check.
-        if (flexBasis->GetUnit() != eStyleUnit_Enumerated) {
-          blockStyleCoord = flexBasis;
-        }
-      }
-    }
+    SetCoordToFlexBasis(isInlineFlexItem, false, flexBasis,
+                        &inlineStyleCoord, &blockStyleCoord);
   }
 
   // Compute inline-axis size
@@ -4949,31 +4983,10 @@ nsFrame::ComputeSizeWithIntrinsicDimensions(nsRenderingContext*  aRenderingConte
       } else {
         blockStyleCoord = imposedMainSizeStyleCoord.ptr();
       }
-
     } else {
-      // Flex items use their "flex-basis" property in place of their main-size
-      // property (e.g. "width") for sizing purposes, *unless* they have
-      // "flex-basis:auto", in which case they use their main-size property
-      // after all.
-      // NOTE: The logic here should match the similar chunk for determining
-      // inlineStyleCoord and blockStyleCoord in nsFrame::ComputeSize().
       const nsStyleCoord* flexBasis = &(stylePos->mFlexBasis);
-      if (flexBasis->GetUnit() != eStyleUnit_Auto) {
-        if (isInlineFlexItem) {
-          inlineStyleCoord = flexBasis;
-        } else {
-          // One caveat for vertical flex items: We don't support enumerated
-          // values (e.g. "max-content") for height properties yet. So, if our
-          // computed flex-basis is an enumerated value, we'll just behave as if
-          // it were "auto", which means "use the main-size property after all"
-          // (which is "height", in this case).
-          // NOTE: Once we support intrinsic sizing keywords for "height",
-          // we should remove this check.
-          if (flexBasis->GetUnit() != eStyleUnit_Enumerated) {
-            blockStyleCoord = flexBasis;
-          }
-        }
-      }
+      SetCoordToFlexBasis(isInlineFlexItem, true, flexBasis,
+                          &inlineStyleCoord, &blockStyleCoord);
     }
   }
 
diff --git a/layout/generic/nsFrame.h b/layout/generic/nsFrame.h
index d75555fec2..d703a62942 100644
--- a/layout/generic/nsFrame.h
+++ b/layout/generic/nsFrame.h
@@ -266,6 +266,17 @@ public:
   virtual mozilla::IntrinsicSize GetIntrinsicSize() override;
   virtual mozilla::AspectRatio GetIntrinsicRatio() override;
 
+  /**
+   * Helper function for determining if flex items should use their
+   * 'flex-basis' property instead of their main-size property, such
+   * as 'width', for sizing purposes.
+   */
+  void SetCoordToFlexBasis(bool aIsInlineFlexItem,
+                           bool aIntrinsic,
+                           const nsStyleCoord* aFlexBasis,
+                           const nsStyleCoord** aInlineStyle,
+                           const nsStyleCoord** aBlockStyle);
+
   virtual mozilla::LogicalSize
   ComputeSize(nsRenderingContext*         aRenderingContext,
               mozilla::WritingMode        aWM,
@@ -295,7 +306,7 @@ public:
   // Compute tight bounds assuming this frame honours its border, background
   // and outline, its children's tight bounds, and nothing else.
   nsRect ComputeSimpleTightBounds(mozilla::gfx::DrawTarget* aDrawTarget) const;
-  
+
   /**
    * A helper, used by |nsFrame::ComputeSize| (for frames that need to
    * override only this part of ComputeSize), that computes the size
diff --git a/layout/generic/nsGridContainerFrame.cpp b/layout/generic/nsGridContainerFrame.cpp
index 0af05be509..0a953d6fff 100644
--- a/layout/generic/nsGridContainerFrame.cpp
+++ b/layout/generic/nsGridContainerFrame.cpp
@@ -2622,9 +2622,9 @@ nsGridContainerFrame::GridReflowInput::CalculateTrackSizes(
   const LogicalSize& aContentBox,
   SizingConstraint   aConstraint)
 {
-  mCols.Initialize(mColFunctions, mGridStyle->mGridColumnGap,
+  mCols.Initialize(mColFunctions, mGridStyle->mColumnGap,
                    aGrid.mGridColEnd, aContentBox.ISize(mWM));
-  mRows.Initialize(mRowFunctions, mGridStyle->mGridRowGap,
+  mRows.Initialize(mRowFunctions, mGridStyle->mRowGap,
                    aGrid.mGridRowEnd, aContentBox.BSize(mWM));
 
   mCols.CalculateSizes(*this, mGridItems, mColFunctions,
@@ -3378,7 +3378,7 @@ nsGridContainerFrame::Grid::PlaceGridItems(GridReflowInput& aState,
   // to a 0,0 based grid after placing definite lines.
   auto areas = gridStyle->mGridTemplateAreas.get();
   uint32_t numRepeatCols = aState.mColFunctions.InitRepeatTracks(
-                             gridStyle->mGridColumnGap,
+                             gridStyle->mColumnGap,
                              aComputedMinSize.ISize(aState.mWM),
                              aComputedSize.ISize(aState.mWM),
                              aComputedMaxSize.ISize(aState.mWM));
@@ -3387,7 +3387,7 @@ nsGridContainerFrame::Grid::PlaceGridItems(GridReflowInput& aState,
   LineNameMap colLineNameMap(gridStyle->mGridTemplateColumns, numRepeatCols);
 
   uint32_t numRepeatRows = aState.mRowFunctions.InitRepeatTracks(
-                             gridStyle->mGridRowGap,
+                             gridStyle->mRowGap,
                              aComputedMinSize.BSize(aState.mWM),
                              aComputedSize.BSize(aState.mWM),
                              aComputedMaxSize.BSize(aState.mWM));
@@ -6214,6 +6214,11 @@ nsGridContainerFrame::Reflow(nsPresContext*           aPresContext,
                           computedISize, bSize);
 
   if (!prevInFlow) {
+    if (computedBSize == NS_AUTOHEIGHT && stylePos->mRowGap.HasPercent()) {
+      // Re-resolve the row-gap now that we know our intrinsic block-size.
+      gridReflowInput.mRows.mGridGap =
+        nsLayoutUtils::ResolveGapToLength(stylePos->mRowGap, bSize);
+    }
     // Apply 'align/justify-content' to the grid.
     // CalculateTrackSizes did the columns.
     gridReflowInput.mRows.AlignJustifyContent(stylePos, wm, contentArea.Size(wm));
@@ -6585,7 +6590,7 @@ nsGridContainerFrame::IntrinsicISize(nsRenderingContext* aRenderingContext,
   if (grid.mGridColEnd == 0) {
     return 0;
   }
-  state.mCols.Initialize(state.mColFunctions, state.mGridStyle->mGridColumnGap,
+  state.mCols.Initialize(state.mColFunctions, state.mGridStyle->mColumnGap,
                          grid.mGridColEnd, NS_UNCONSTRAINEDSIZE);
   auto constraint = aType == nsLayoutUtils::MIN_ISIZE ?
     SizingConstraint::eMinContent : SizingConstraint::eMaxContent;
@@ -6593,7 +6598,7 @@ nsGridContainerFrame::IntrinsicISize(nsRenderingContext* aRenderingContext,
                              NS_UNCONSTRAINEDSIZE, &GridArea::mCols,
                              constraint);
   state.mCols.mGridGap =
-    nsLayoutUtils::ResolveGapToLength(state.mGridStyle->mGridColumnGap,
+    nsLayoutUtils::ResolveGapToLength(state.mGridStyle->mColumnGap,
                                       NS_UNCONSTRAINEDSIZE);
   nscoord length = 0;
   for (const TrackSize& sz : state.mCols.mSizes) {
diff --git a/layout/reftests/bugs/reftest.list b/layout/reftests/bugs/reftest.list
index 4fb75edab3..e6cc895d94 100644
--- a/layout/reftests/bugs/reftest.list
+++ b/layout/reftests/bugs/reftest.list
@@ -1841,7 +1841,7 @@ fuzzy-if(skiaContent,1,24000) == 1025914-1.html 1025914-1-ref.html
 == 1050493-1.html 1050493-1-ref.html
 == 1050788-1.html about:blank
 == 1053035-1-flex.html 1053035-1-ref.html
-test-pref(layout.css.grid.enabled,true) == 1053035-1-grid.html 1053035-1-ref.html
+== 1053035-1-grid.html 1053035-1-ref.html
 == 1059167-1.html 1059167-1-ref.html
 == 1059498-1.html 1059498-1-ref.html
 == 1059498-2.html 1059498-1-ref.html
diff --git a/layout/reftests/css-grid/grid-percent-grid-gap-001-ref.html b/layout/reftests/css-grid/grid-percent-grid-gap-001-ref.html
index 7ad85e1e58..1970d10e37 100644
--- a/layout/reftests/css-grid/grid-percent-grid-gap-001-ref.html
+++ b/layout/reftests/css-grid/grid-percent-grid-gap-001-ref.html
@@ -65,7 +65,7 @@ br { clear: both; }
 </div>
 
 <div class="float">
-<div class="grid" style="width:60px; height:60px; grid-column-gap:12px">
+<div class="grid" style="width:60px; height:60px; gap:12px">
   <span><x></x></span>
   <span><x></x></span>
   <span><x></x></span>
@@ -74,7 +74,7 @@ br { clear: both; }
 </div>
 
 <div class="inline-grid">
-<div class="grid" style="width:60px; height:60px; grid-column-gap:12px; align-self:start; justify-self:start;">
+<div class="grid" style="width:60px; height:60px; gap:12px; align-self:start; justify-self:start;">
   <span><x></x></span>
   <span><x></x></span>
   <span><x></x></span>
@@ -142,7 +142,7 @@ br { clear: both; }
 </div>
 
 <div class="float" style="margin-top:-50px; width:62px">
-<div class="grid" style="padding-left:186px; height:60px; grid-column-gap:calc(186px * 0.2);">
+<div class="grid" style="padding-left:186px; height:60px; gap:12px calc(186px * 0.2);">
   <span style="margin-left:-186px; width:30px"><x></x></span>
   <span style="margin-left:-186px; width:30px"><x></x></span>
   <span style="margin-left:-186px; width:30px"><x></x></span>
diff --git a/layout/reftests/css-grid/grid-repeat-auto-fill-fit-002-ref.html b/layout/reftests/css-grid/grid-repeat-auto-fill-fit-002-ref.html
index 682e0ca38e..8de84391eb 100644
--- a/layout/reftests/css-grid/grid-repeat-auto-fill-fit-002-ref.html
+++ b/layout/reftests/css-grid/grid-repeat-auto-fill-fit-002-ref.html
@@ -83,15 +83,18 @@ fill,fit {
 
 .zero-progress {
   grid-row-gap: calc(10px - 1%);
-  grid-template-rows: [a] 10px repeat(3, [b] 0 [c]) [d];
+  grid-template-rows: [a] 10px repeat(3, [b] calc(4px / 10) [c]) [d];
+  height:40px;
 }
 .w50.zero-progress {
   grid-row-gap: calc(10px - 1%);
   grid-template-rows: [a] 10px repeat(3, [b] 0 [c]) [d];
+  height:50px;
 }
 .mw50.zero-progress {
   grid-row-gap: calc(10px - 1%);
-  grid-template-rows: [a] 10px repeat(4, [b] 0 [c]) [d];
+  grid-template-rows: [a] 10px repeat(4, [b] calc(5px / 10) [c]) [d];
+  height:50px;
 }
 </style>
 </head>
diff --git a/layout/reftests/css-grid/reftest.list b/layout/reftests/css-grid/reftest.list
index 35e3140a85..62a397b540 100644
--- a/layout/reftests/css-grid/reftest.list
+++ b/layout/reftests/css-grid/reftest.list
@@ -1,5 +1,3 @@
-default-preferences pref(layout.css.grid.enabled,true)
-
 fails == grid-whitespace-handling-1a.xhtml grid-whitespace-handling-1-ref.xhtml
 fails == grid-whitespace-handling-1b.xhtml grid-whitespace-handling-1-ref.xhtml
 == grid-whitespace-handling-2.xhtml  grid-whitespace-handling-2-ref.xhtml
diff --git a/layout/reftests/flexbox/flexbox-table-flex-items-2-ref.html b/layout/reftests/flexbox/flexbox-table-flex-items-2-ref.html
new file mode 100644
index 0000000000..98a93716a5
--- /dev/null
+++ b/layout/reftests/flexbox/flexbox-table-flex-items-2-ref.html
@@ -0,0 +1,64 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>CSS Reftest Reference</title>
+  <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+  <link rel="help" href="https://www.w3.org/TR/css-flexbox-1/#flex-base-size">
+  <style>
+  .container {
+    display: flex;
+    width: 100px;
+    border: 1px solid black;
+  }
+
+  /* Two types of flex items: */
+  .table {
+    border: 2px solid teal;
+  }
+  .block {
+    border: 2px solid brown;
+  }
+
+  /* Each flex item gets one of these as its contents,
+     to have a nonzero content size: */
+  ib {
+    display: inline-block;
+    background: blue;
+    border: 1px solid gray;
+    width: 15px;
+    height: 10px;
+  }
+  </style>
+</head>
+<body>
+<!-- auto size: -->
+<div class="container">
+  <div class="table"><ib></ib></div>
+  <div class="block"><ib></ib></div>
+</div>
+
+<!-- px size: -->
+<div class="container">
+  <div class="table" style="width: 30px"><ib></ib></div>
+  <div class="block" style="width: 30px"><ib></ib></div>
+</div>
+
+<!-- % size: -->
+<div class="container">
+  <div class="table" style="width: 30%"><ib></ib></div>
+  <div class="block" style="width: 30%"><ib></ib></div>
+</div>
+
+<!-- calc() size: -->
+<div class="container">
+  <div class="table" style="width: calc(10px + 20%)"><ib></ib></div>
+  <div class="block" style="width: calc(10px + 20%)"><ib></ib></div>
+</div>
+
+</body>
+</html>
diff --git a/layout/reftests/flexbox/flexbox-table-flex-items-2.html b/layout/reftests/flexbox/flexbox-table-flex-items-2.html
new file mode 100644
index 0000000000..c11ce70802
--- /dev/null
+++ b/layout/reftests/flexbox/flexbox-table-flex-items-2.html
@@ -0,0 +1,73 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>
+    CSS Test: Testing that implicit "flex-basis: content" on table wrapper box
+    doesn't prevent explicit table size from influencing flex base size.
+  </title>
+  <!-- XXXdholbert NOTE: This probably eventually should move to our
+       upstreamed reftest directory.  But for now, this is just asserting
+       backwards-compatible/interoperable (but not necessary spec-compliant)
+       behavior, per https://github.com/w3c/csswg-drafts/issues/2604 -->
+  <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+  <link rel="help" href="https://www.w3.org/TR/css-flexbox-1/#flex-base-size">
+  <link rel="match" href="flexbox-table-flex-items-2.html">
+  <style>
+  .container {
+    display: flex;
+    width: 100px;
+    border: 1px solid black;
+  }
+
+  /* Two types of flex items: */
+  .table {
+    display: table;
+    border: 2px solid teal;
+  }
+  .block {
+    border: 2px solid brown;
+  }
+
+  /* Each flex item gets one of these as its contents,
+     to have a nonzero content size: */
+  ib {
+    display: inline-block;
+    background: blue;
+    border: 1px solid gray;
+    width: 15px;
+    height: 10px;
+  }
+  </style>
+</head>
+<body>
+<!-- auto size: -->
+<div class="container">
+  <div class="table"><ib></ib></div>
+  <div class="block"><ib></ib></div>
+</div>
+
+<!-- px size: -->
+<div class="container">
+  <div class="table" style="width: 30px"><ib></ib></div>
+  <div class="block" style="width: 30px"><ib></ib></div>
+</div>
+
+<!-- % size: -->
+<div class="container">
+  <div class="table" style="width: 30%"><ib></ib></div>
+  <div class="block" style="width: 30%"><ib></ib></div>
+</div>
+
+<!-- calc() size: -->
+<div class="container">
+  <div class="table" style="width: calc(10px + 20%)"><ib></ib></div>
+  <div class="block" style="width: calc(10px + 20%)"><ib></ib></div>
+</div>
+
+</body>
+</html>
diff --git a/layout/reftests/flexbox/flexbox-table-flex-items-3-ref.html b/layout/reftests/flexbox/flexbox-table-flex-items-3-ref.html
new file mode 100644
index 0000000000..568495f341
--- /dev/null
+++ b/layout/reftests/flexbox/flexbox-table-flex-items-3-ref.html
@@ -0,0 +1,66 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>CSS Reftest Reference</title>
+  <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+  <link rel="help" href="https://www.w3.org/TR/css-flexbox-1/#flex-base-size">
+  <style>
+  .container {
+    display: flex;
+    flex-direction: column;
+    height: 100px;
+    float: left;
+    border: 1px solid black;
+  }
+
+  /* Two types of flex items: */
+  .table {
+    border: 2px solid teal;
+  }
+  .block {
+    border: 2px solid brown;
+  }
+
+  /* Each flex item gets one of these as its contents,
+     to have a nonzero content size: */
+  ib {
+    display: inline-block;
+    background: blue;
+    border: 1px solid gray;
+    width: 15px;
+    height: 10px;
+  }
+  </style>
+</head>
+<body>
+<!-- auto size: -->
+<div class="container">
+  <div class="table"><ib></ib></div>
+  <div class="block"><ib></ib></div>
+</div>
+
+<!-- px size: -->
+<div class="container">
+  <div class="table" style="height: 30px"><ib></ib></div>
+  <div class="block" style="height: 30px"><ib></ib></div>
+</div>
+
+<!-- % size: -->
+<div class="container">
+  <div class="table" style="height: 30%"><ib></ib></div>
+  <div class="block" style="height: 30%"><ib></ib></div>
+</div>
+
+<!-- calc() size: -->
+<div class="container">
+  <div class="table" style="height: calc(10px + 20%)"><ib></ib></div>
+  <div class="block" style="height: calc(10px + 20%)"><ib></ib></div>
+</div>
+
+</body>
+</html>
diff --git a/layout/reftests/flexbox/flexbox-table-flex-items-3.html b/layout/reftests/flexbox/flexbox-table-flex-items-3.html
new file mode 100644
index 0000000000..c68152856f
--- /dev/null
+++ b/layout/reftests/flexbox/flexbox-table-flex-items-3.html
@@ -0,0 +1,75 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>
+    CSS Test: Testing that implicit "flex-basis: content" on table wrapper box
+    doesn't prevent explicit table size from influencing flex base size.
+  </title>
+  <!-- XXXdholbert NOTE: This probably eventually should move to our
+       upstreamed reftest directory.  But for now, this is just asserting
+       backwards-compatible/interoperable (but not necessary spec-compliant)
+       behavior, per https://github.com/w3c/csswg-drafts/issues/2604 -->
+  <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+  <link rel="help" href="https://www.w3.org/TR/css-flexbox-1/#flex-base-size">
+  <link rel="match" href="flexbox-table-flex-items-3.html">
+  <style>
+  .container {
+    display: flex;
+    flex-direction: column;
+    height: 100px;
+    float: left;
+    border: 1px solid black;
+  }
+
+  /* Two types of flex items: */
+  .table {
+    display: table;
+    border: 2px solid teal;
+  }
+  .block {
+    border: 2px solid brown;
+  }
+
+  /* Each flex item gets one of these as its contents,
+     to have a nonzero content size: */
+  ib {
+    display: inline-block;
+    background: blue;
+    border: 1px solid gray;
+    width: 15px;
+    height: 10px;
+  }
+  </style>
+</head>
+<body>
+<!-- auto size: -->
+<div class="container">
+  <div class="table"><ib></ib></div>
+  <div class="block"><ib></ib></div>
+</div>
+
+<!-- px size: -->
+<div class="container">
+  <div class="table" style="height: 30px"><ib></ib></div>
+  <div class="block" style="height: 30px"><ib></ib></div>
+</div>
+
+<!-- % size: -->
+<div class="container">
+  <div class="table" style="height: 30%"><ib></ib></div>
+  <div class="block" style="height: 30%"><ib></ib></div>
+</div>
+
+<!-- calc() size: -->
+<div class="container">
+  <div class="table" style="height: calc(10px + 20%)"><ib></ib></div>
+  <div class="block" style="height: calc(10px + 20%)"><ib></ib></div>
+</div>
+
+</body>
+</html>
diff --git a/layout/reftests/flexbox/reftest.list b/layout/reftests/flexbox/reftest.list
index be156100e8..075b789026 100644
--- a/layout/reftests/flexbox/reftest.list
+++ b/layout/reftests/flexbox/reftest.list
@@ -116,3 +116,5 @@ fuzzy-if(gtkWidget,1,31) == flexbox-widget-flex-items-4.html flexbox-widget-flex
 
 # Tests for table flex items
 == flexbox-table-flex-items-1-ref.html flexbox-table-flex-items-1-ref.html
+== flexbox-table-flex-items-2.html flexbox-table-flex-items-2-ref.html
+== flexbox-table-flex-items-3.html flexbox-table-flex-items-3-ref.html
diff --git a/layout/reftests/list-item/reftest.list b/layout/reftests/list-item/reftest.list
index c47473d0b2..a795dfdf4e 100644
--- a/layout/reftests/list-item/reftest.list
+++ b/layout/reftests/list-item/reftest.list
@@ -1,6 +1,6 @@
 fuzzy-if(OSX>=1008,55,4) == numbering-1.html numbering-1-ref.html
 == numbering-2.html numbering-2-ref.html
-pref(layout.css.grid.enabled,true) fuzzy-if(OSX>=1008,8,1) == numbering-3.html numbering-3-ref.html
+fuzzy-if(OSX>=1008,8,1) == numbering-3.html numbering-3-ref.html
 fuzzy-if(OSX>=1008,72,2) == numbering-4.html numbering-4-ref.html
 == ol-reversed-1a.html ol-reversed-1-ref.html
 asserts(1) == ol-reversed-1b.html ol-reversed-1-ref.html # bug 478135
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-001-ref.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-001-ref.html
new file mode 100644
index 0000000000..0606afe539
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-001-ref.html
@@ -0,0 +1,97 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0
+-->
+<!--
+     Reference for the correctness of gaps in horizontal and vertical multi-line
+     flex containers.
+-->
+<html>
+<head>
+  <title>Reference: Testing row and column gaps in horizontal and vertical multi-line flex containers with the space-around property and auto margins</title>
+  <link rel="author" title="Mihir Iyer" href="mailto:miyer@mozilla.com">
+  <meta charset="utf-8">
+  <style>
+    .outerBox {
+      width: 200px;
+      height: 220px;
+      border: 1px solid black;
+      float: left;
+    }
+    .flexContainer {
+      display: flex;
+      align-content: space-around;
+      justify-content: space-around;
+    }
+    .rowNoWrap {
+      flex-flow: row nowrap;
+    }
+    .columnNoWrap {
+      flex-flow: column nowrap;
+    }
+    .item {
+      border: 1px solid blue;
+      background: lightblue;
+      width: 28px;
+      height: 28px;
+    }
+    .autoLBMargins {
+      margin-left: auto;
+      margin-bottom: auto;
+    }
+    .autoBMargin {
+      margin-bottom: auto;
+    }
+    .right20 {
+      margin-right: 20px;
+    }
+    .bottom40 {
+      margin-bottom: 40px;
+    }
+    .tb30100 {
+      margin-top: 30px;
+      margin-bottom: 100px;
+    }
+    .lr3080 {
+      margin-left: 30px;
+      margin-right: 80px;
+    }
+    .w200 {
+      width: 200px;
+    }
+    .h220 {
+      height: 220px;
+    }
+    .fleft {
+      float: left;
+    }
+  </style>
+</head>
+<body>
+  <div class="outerBox">
+    <div class="flexContainer w200 rowNoWrap tb30100">
+      <div class="item right20"></div>
+      <div class="item right20"></div>
+      <div class="item right20"></div>
+      <div class="item"></div>
+    </div>
+    <div class="flexContainer w200 rowNoWrap">
+      <div class="item autoLBMargins right20"></div>
+      <div class="item"></div>
+    </div>
+  </div>
+  <div class="outerBox">
+    <div class="flexContainer fleft h220 columnNoWrap lr3080">
+      <div class="item bottom40"></div>
+      <div class="item bottom40"></div>
+      <div class="item"></div>
+    </div>
+    <div class="flexContainer fleft  h220 columnNoWrap">
+      <div class="item bottom40"></div>
+      <div class="item bottom40"></div>
+      <div class="item autoBMargin"></div>
+    </div>
+  </div>
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-001.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-001.html
new file mode 100644
index 0000000000..25b28e8094
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-001.html
@@ -0,0 +1,65 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0
+-->
+<!--
+     Testcase for the correctness of gaps in horizontal and vertical multi-line
+     flex containers.
+-->
+<html>
+<head>
+  <title>CSS Test: Testing row and column gaps in horizontal and vertical multi-line flex containers with the space-around property and auto margins</title>
+  <link rel="author" title="Mihir Iyer" href="mailto:miyer@mozilla.com">
+  <link rel="help" href="https://drafts.csswg.org/css-align/#gap-flex">
+  <link rel="match" href="flexbox-column-row-gap-001-ref.html">
+  <meta charset="utf-8">
+  <style>
+    .flexContainer {
+      display: flex;
+      width: 200px;
+      height: 220px;
+      border: 1px solid black;
+      column-gap: 10%;
+      row-gap: 40px;
+      align-content: space-around;
+      justify-content: space-around;
+      float: left;
+    }
+    .rowWrap {
+      flex-flow: row wrap;
+    }
+    .columnWrap {
+      flex-flow: column wrap;
+    }
+    .item {
+      border: 1px solid blue;
+      background: lightblue;
+      width: 28px;
+      height: 28px;
+    }
+    .autoLBMargins {
+      margin-left: auto;
+      margin-bottom: auto;
+    }
+  </style>
+</head>
+<body>
+  <div class="flexContainer rowWrap">
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item autoLBMargins"></div>
+    <div class="item"></div>
+  </div>
+  <div class="flexContainer columnWrap">
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item autoLBMargins"></div>
+  </div>
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-002-ref.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-002-ref.html
new file mode 100644
index 0000000000..e23ddfe261
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-002-ref.html
@@ -0,0 +1,67 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0
+-->
+<!--
+     Testcase for the correctness of gaps in vertical writing mode
+     multi-line flex containers.
+-->
+<html>
+<head>
+  <title>Reference: Testing row and column gaps in vertical writing mode multi-line flex containers</title>
+  <link rel="author" title="Mihir Iyer" href="mailto:miyer@mozilla.com">
+  <meta charset="utf-8">
+  <style>
+    .flexContainer {
+      display: flex;
+      width: 220px;
+      height: 200px;
+      border: 1px solid black;
+      align-content: flex-start;
+      justify-content: flex-end;
+      float: left;
+      writing-mode: vertical-lr;
+    }
+    .rowWrap {
+      flex-flow: row wrap;
+    }
+    .columnWrap {
+      flex-flow: column wrap;
+    }
+    .item {
+      border: 1px solid blue;
+      background: lightblue;
+      width: 28px;
+      height: 28px;
+    }
+    .b20 {
+      margin-bottom: 20px;
+    }
+    .t20 {
+      margin-top: 20px;
+    }
+    .l10 {
+      margin-left: 10px;
+    }
+  </style>
+</head>
+<body>
+  <div class="flexContainer rowWrap">
+    <div class="item b20"></div>
+    <div class="item b20"></div>
+    <div class="item b20"></div>
+    <div class="item"></div>
+    <div class="item l10 b20"></div>
+    <div class="item l10"></div>
+  </div>
+  <div class="flexContainer columnWrap">
+    <div class="item"></div>
+    <div class="item l10"></div>
+    <div class="item l10"></div>
+    <div class="item l10"></div>
+    <div class="item l10"></div>
+    <div class="item l10 t20"></div>
+  </div>
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-002.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-002.html
new file mode 100644
index 0000000000..fcd19cf8d4
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-002.html
@@ -0,0 +1,62 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0
+-->
+<!--
+     Testcase for the correctness of gaps in vertical writing mode multi-line
+     flex containers.
+-->
+<html>
+<head>
+  <title>CSS Test: Testing row and column gaps in vertical writing mode multi-line flex containers</title>
+  <link rel="author" title="Mihir Iyer" href="mailto:miyer@mozilla.com">
+  <link rel="help" href="https://drafts.csswg.org/css-align/#gap-flex">
+  <link rel="match" href="flexbox-column-row-gap-002-ref.html">
+  <meta charset="utf-8">
+  <style>
+    .flexContainer {
+      display: flex;
+      width: 220px;
+      height: 200px;
+      border: 1px solid black;
+      column-gap: 10%;
+      row-gap: 10px;
+      align-content: flex-start;
+      justify-content: flex-end;
+      float: left;
+      writing-mode: vertical-lr;
+    }
+    .rowWrap {
+      flex-flow: row wrap;
+    }
+    .columnWrap {
+      flex-flow: column wrap;
+    }
+    .item {
+      border: 1px solid blue;
+      background: lightblue;
+      width: 28px;
+      height: 28px;
+    }
+  </style>
+</head>
+<body>
+  <div class="flexContainer rowWrap">
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+  </div>
+  <div class="flexContainer columnWrap">
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+  </div>
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-003-ref.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-003-ref.html
new file mode 100644
index 0000000000..6e7f220b44
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-003-ref.html
@@ -0,0 +1,63 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0
+-->
+<html>
+<head>
+  <title>Reference: Testing cross size computation with row and column gaps in horizontal multi-line flex containers</title>
+  <link rel="author" title="Mihir Iyer" href="mailto:miyer@mozilla.com">
+  <meta charset="utf-8">
+</html>
+  <style>
+    .flexContainer {
+      display: flex;
+      border: 1px solid black;
+      column-gap: 20px;
+      row-gap: 40px;
+      align-content: space-around;
+      justify-content: space-around;
+    }
+    .rowWrap {
+      flex-flow: row wrap;
+    }
+    .item {
+      border: 1px solid blue;
+      background: lightblue;
+      width: 28px;
+      height: 28px;
+    }
+    .autoLBMargins {
+      margin-left: auto;
+      margin-bottom: auto;
+    }
+    .w200 {
+      width: 200px;
+    }
+    .h100 {
+      height: 100px;
+    }
+    .h90 {
+      height: 90px;
+    }
+  </style>
+</head>
+<body>
+  <div class="flexContainer rowWrap w200 h100">
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item autoLBMargins"></div>
+    <div class="item"></div>
+  </div>
+  <div class="flexContainer rowWrap w200 h90">
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item autoLBMargins"></div>
+    <div class="item"></div>
+  </div>
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-003.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-003.html
new file mode 100644
index 0000000000..2dcd027173
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-003.html
@@ -0,0 +1,61 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0
+-->
+<html>
+<head>
+  <title>CSS Test: Testing cross size computation with row and column gaps in horizontal multi-line flex containers</title>
+  <link rel="author" title="Mihir Iyer" href="mailto:miyer@mozilla.com">
+  <link rel="help" href="https://drafts.csswg.org/css-align/#gap-flex">
+  <link rel="match" href="flexbox-column-row-gap-003-ref.html">
+  <meta charset="utf-8">
+  <style>
+    .flexContainer {
+      display: flex;
+      border: 1px solid black;
+      column-gap: 20px;
+      row-gap: 40px;
+      align-content: space-around;
+      justify-content: space-around;
+    }
+    .rowWrap {
+      flex-flow: row wrap;
+    }
+    .item {
+      border: 1px solid blue;
+      background: lightblue;
+      width: 28px;
+      height: 28px;
+    }
+    .autoLBMargins {
+      margin-left: auto;
+      margin-bottom: auto;
+    }
+    .w200 {
+      width: 200px;
+    }
+    .hclamp {
+      max-height: 90px;
+    }
+  </style>
+</head>
+<body>
+  <div class="flexContainer rowWrap w200">
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item autoLBMargins"></div>
+    <div class="item"></div>
+  </div>
+  <div class="flexContainer rowWrap w200 hclamp">
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item"></div>
+    <div class="item autoLBMargins"></div>
+    <div class="item"></div>
+  </div>
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-004-ref.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-004-ref.html
new file mode 100644
index 0000000000..0b40fb2d62
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-004-ref.html
@@ -0,0 +1,68 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0
+-->
+<html>
+<head>
+  <title>Reference: Testing percentage gap resolution in flex containers</title>
+  <link rel="author" title="Mihir Iyer" href="mailto:miyer@mozilla.com">
+  <meta charset="utf-8">
+  <style>
+    .flexContainer {
+      display: flex;
+      border: 2px solid black;
+      column-gap: 10px;
+      align-content: start;
+      justify-content: start;
+      margin-top: 20px;
+    }
+    .item {
+      border: 1px solid blue;
+      background: yellow;
+      width: 48px;
+      height: 48px;
+      flex: none;
+    }
+    .vertLR {
+      writing-mode: vertical-lr;
+    }
+    .rowWrap {
+      flex-flow: row wrap;
+    }
+    .colWrap {
+      flex-flow: column wrap;
+    }
+    .w50 {
+      width: 50px;
+    }
+    .h100 {
+      height: 100px;
+    }
+    .w100 {
+      width: 100px;
+    }
+    .noWrap {
+      flex-wrap: nowrap;
+    }
+  </style>
+</head>
+<body>
+  <div class="flexContainer rowWrap w50 h100">
+    <div class="item"></div>
+    <div class="item"></div>
+  </div>
+  <div class="flexContainer colWrap w50 h100 noWrap">
+    <div class="item"></div>
+    <div class="item"></div>
+  </div>
+  <div class="flexContainer vertLR rowWrap h100 w100">
+    <div class="item"></div>
+    <div class="item"></div>
+  </div>
+  <div class="flexContainer vertLR colWrap w100 noWrap">
+    <div class="item"></div>
+    <div class="item"></div>
+  </div>
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-004.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-004.html
new file mode 100644
index 0000000000..0d86b3818f
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-column-row-gap-004.html
@@ -0,0 +1,64 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0
+-->
+<html>
+<head>
+  <title>CSS Test: Testing percentage gap resolution in flex containers</title>
+  <link rel="author" title="Mihir Iyer" href="mailto:miyer@mozilla.com">
+  <link rel="help" href="https://drafts.csswg.org/css-align/#column-row-gap">
+  <link rel="match" href="flexbox-column-row-gap-004-ref.html">
+  <link rel="help" href="https://github.com/w3c/csswg-drafts/issues/5081">
+  <meta charset="utf-8">
+  <meta name="assert" content="% row-gaps in a flexbox with indefinite block size are treated as 'normal'." />
+  <style>
+    .flexContainer {
+      display: flex;
+      border: 2px solid black;
+      row-gap: 20%;
+      column-gap: 10%;
+      align-content: start;
+      justify-content: start;
+      margin-top: 20px;
+    }
+    .item {
+      border: 1px solid blue;
+      background: yellow;
+      width: 48px;
+      height: 48px;
+      flex: none;
+    }
+    .vertLR {
+      writing-mode: vertical-lr;
+    }
+    .rowWrap {
+      flex-flow: row wrap;
+    }
+    .colWrap {
+      flex-flow: column wrap;
+    }
+    .w50 {
+      width: 50px;
+    }
+  </style>
+</head>
+<body>
+  <div class="flexContainer rowWrap w50">
+    <div class="item"></div>
+    <div class="item"></div>
+  </div>
+  <div class="flexContainer colWrap w50">
+    <div class="item"></div>
+    <div class="item"></div>
+  </div>
+  <div class="flexContainer vertLR rowWrap">
+    <div class="item"></div>
+    <div class="item"></div>
+  </div>
+  <div class="flexContainer vertLR colWrap">
+    <div class="item"></div>
+    <div class="item"></div>
+  </div>
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-001-ref.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-001-ref.html
new file mode 100644
index 0000000000..b537711020
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-001-ref.html
@@ -0,0 +1,77 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>CSS Reftest Reference</title>
+  <meta charset="utf-8">
+  <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+  <link rel="stylesheet" type="text/css" href="support/ahem.css">
+  <style>
+  .container {
+    display: flex;
+    flex-direction: row;
+    justify-content: space-between;
+    border: 2px solid purple;
+    padding: 2px;
+    margin-bottom: 2em;
+    height: 50px;
+    width: 200px;
+  }
+
+  .container > * {
+    flex-shrink: 0;
+    min-width: 0;
+    border: 2px solid teal;
+  }
+
+  .smallText { font: 10px Ahem; }
+  .bigText   { font: 20px Ahem; }
+  .spacerChild::before {
+    content: '';
+    display: block;
+    background: brown;
+    height: 10px;
+    width: 10px;
+  }
+  .justPadding {
+    /* Empty div with 5px padding on each side */
+    padding: 5px;
+    background: cyan;
+  }
+  canvas { background: fuchsia }
+  </style>
+</head>
+<body>
+<!-- Flex items have unspecified size properties: -->
+<div class="container">
+  <div class="smallText">a b</div>
+  <div class="bigText">c</div>
+  <div class="spacerChild"></div>
+  <div class="justPadding"></div>
+  <canvas width="20"></canvas>
+</div>
+
+<!-- Various specified main-size values, in testcase
+     (removed here in reference case, because they shouldn't affect sizing): -->
+<div class="container">
+  <div class="smallText">a b</div>
+  <div class="bigText">c</div>
+  <div class="spacerChild"></div>
+  <div class="justPadding"></div>
+  <canvas width="20"></canvas>
+</div>
+
+<!-- Various specified cross-size values (should be honored): -->
+<div class="container">
+  <div class="smallText"    style="height: 0px">a b</div>
+  <div class="bigText"      style="height: 40px">c</div>
+  <div class="spacerChild"  style="height: 20px"></div>
+  <div class="justPadding"  style="height: 10px"></div>
+  <canvas width="20"        style="height: 8px"></canvas>
+</div>
+
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-001a.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-001a.html
new file mode 100644
index 0000000000..4227f68ff1
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-001a.html
@@ -0,0 +1,83 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>
+    CSS Test: Testing "flex-basis: content" in a row-oriented flex container
+  </title>
+  <meta charset="utf-8">
+  <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+  <link rel="help" href="https://www.w3.org/TR/css-flexbox-1/#propdef-flex-basis">
+  <link rel="match" href="flexbox-flex-basis-content-001-ref.html">
+  <link rel="stylesheet" type="text/css" href="support/ahem.css">
+  <style>
+  .container {
+    display: flex;
+    flex-direction: row;
+    justify-content: space-between;
+    border: 2px solid purple;
+    padding: 2px;
+    margin-bottom: 2em;
+    height: 50px;
+    width: 200px;
+  }
+
+  .container > * {
+    /* All flex items have "flex-basis: content" (and zero flex-shrink and
+       min-main-size, to avoid any influence from those). */
+    flex-basis: content;
+    flex-shrink: 0;
+    min-width: 0;
+    border: 2px solid teal;
+  }
+
+  .smallText { font: 10px Ahem; }
+  .bigText   { font: 20px Ahem; }
+  .spacerChild::before {
+    content: '';
+    display: block;
+    background: brown;
+    height: 10px;
+    width: 10px;
+  }
+  .justPadding {
+    /* Empty div with 5px padding on each side */
+    padding: 5px;
+    background: cyan;
+  }
+  canvas { background: fuchsia }
+  </style>
+</head>
+<body>
+<!-- Flex items have unspecified size properties: -->
+<div class="container">
+  <div class="smallText">a b</div>
+  <div class="bigText">c</div>
+  <div class="spacerChild"></div>
+  <div class="justPadding"></div>
+  <canvas width="20"></canvas>
+</div>
+
+<!-- Various specified main-size values (should be ignored): -->
+<div class="container">
+  <div class="smallText"    style="width: 0px">a b</div>
+  <div class="bigText"      style="width: 40px">c</div>
+  <div class="spacerChild"  style="width: 20px"></div>
+  <div class="justPadding"  style="width: 10px"></div>
+  <canvas width="20"        style="width: 8px"></canvas>
+</div>
+
+<!-- Various specified cross-size values (should be honored): -->
+<div class="container">
+  <div class="smallText"    style="height: 0px">a b</div>
+  <div class="bigText"      style="height: 40px">c</div>
+  <div class="spacerChild"  style="height: 20px"></div>
+  <div class="justPadding"  style="height: 10px"></div>
+  <canvas width="20"        style="height: 8px"></canvas>
+</div>
+
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-001b.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-001b.html
new file mode 100644
index 0000000000..489ce65d8f
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-001b.html
@@ -0,0 +1,83 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>
+    CSS Test: Testing "flex-basis: content" (set via the "flex" shorthand)
+    in a row-oriented flex container.
+  </title>
+  <meta charset="utf-8">
+  <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+  <link rel="help" href="https://www.w3.org/TR/css-flexbox-1/#propdef-flex-basis">
+  <link rel="match" href="flexbox-flex-basis-content-001-ref.html">
+  <link rel="stylesheet" type="text/css" href="support/ahem.css">
+  <style>
+  .container {
+    display: flex;
+    flex-direction: row;
+    justify-content: space-between;
+    border: 2px solid purple;
+    padding: 2px;
+    margin-bottom: 2em;
+    height: 50px;
+    width: 200px;
+  }
+
+  .container > * {
+    /* All flex items have "flex-basis: content" (and zero flex-shrink and
+       min-main-size, to avoid any influence from those). */
+    flex: 0 0 content;
+    min-width: 0;
+    border: 2px solid teal;
+  }
+
+  .smallText { font: 10px Ahem; }
+  .bigText   { font: 20px Ahem; }
+  .spacerChild::before {
+    content: '';
+    display: block;
+    background: brown;
+    height: 10px;
+    width: 10px;
+  }
+  .justPadding {
+    /* Empty div with 5px padding on each side */
+    padding: 5px;
+    background: cyan;
+  }
+  canvas { background: fuchsia }
+  </style>
+</head>
+<body>
+<!-- Flex items have unspecified size properties: -->
+<div class="container">
+  <div class="smallText">a b</div>
+  <div class="bigText">c</div>
+  <div class="spacerChild"></div>
+  <div class="justPadding"></div>
+  <canvas width="20"></canvas>
+</div>
+
+<!-- Various specified main-size values (should be ignored): -->
+<div class="container">
+  <div class="smallText"    style="width: 0px">a b</div>
+  <div class="bigText"      style="width: 40px">c</div>
+  <div class="spacerChild"  style="width: 20px"></div>
+  <div class="justPadding"  style="width: 10px"></div>
+  <canvas width="20"        style="width: 8px"></canvas>
+</div>
+
+<!-- Various specified cross-size values (should be honored): -->
+<div class="container">
+  <div class="smallText"    style="height: 0px">a b</div>
+  <div class="bigText"      style="height: 40px">c</div>
+  <div class="spacerChild"  style="height: 20px"></div>
+  <div class="justPadding"  style="height: 10px"></div>
+  <canvas width="20"        style="height: 8px"></canvas>
+</div>
+
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-002-ref.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-002-ref.html
new file mode 100644
index 0000000000..a7d1bcf77b
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-002-ref.html
@@ -0,0 +1,78 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>CSS Reftest Reference</title>
+  <meta charset="utf-8">
+  <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+  <link rel="stylesheet" type="text/css" href="support/ahem.css">
+  <style>
+  .container {
+    display: flex;
+    flex-direction: column;
+    justify-content: space-between;
+    border: 2px solid purple;
+    padding: 2px;
+    margin-right: 2em;
+    width: 50px;
+    height: 200px;
+    float: left;
+  }
+
+  .container > * {
+    flex-shrink: 0;
+    min-height: 0;
+    border: 2px solid teal;
+  }
+
+  .smallText { font: 10px Ahem; }
+  .bigText   { font: 20px Ahem; }
+  .spacerChild::before {
+    content: '';
+    display: block;
+    background: brown;
+    height: 10px;
+    width: 10px;
+  }
+  .justPadding {
+    /* Empty div with 5px padding on each side */
+    padding: 5px;
+    background: cyan;
+  }
+  canvas { background: fuchsia }
+  </style>
+</head>
+<body>
+<!-- Flex items have unspecified size properties: -->
+<div class="container">
+  <div class="smallText">a b</div>
+  <div class="bigText">c</div>
+  <div class="spacerChild"></div>
+  <div class="justPadding"></div>
+  <canvas height="20"></canvas>
+</div>
+
+<!-- Various specified main-size values, in testcase
+     (removed here in reference case, because they shouldn't affect sizing): -->
+<div class="container">
+  <div class="smallText">a b</div>
+  <div class="bigText">c</div>
+  <div class="spacerChild"></div>
+  <div class="justPadding"></div>
+  <canvas height="20"></canvas>
+</div>
+
+<!-- Various specified cross-size values (should be honored): -->
+<div class="container">
+  <div class="smallText"    style="width: 0px">a b</div>
+  <div class="bigText"      style="width: 40px">c</div>
+  <div class="spacerChild"  style="width: 20px"></div>
+  <div class="justPadding"  style="width: 10px"></div>
+  <canvas height="20"       style="width: 8px"></canvas>
+</div>
+
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-002a.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-002a.html
new file mode 100644
index 0000000000..481a3f2290
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-002a.html
@@ -0,0 +1,84 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>
+    CSS Test: Testing "flex-basis: content" in a column-oriented flex container
+  </title>
+  <meta charset="utf-8">
+  <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+  <link rel="help" href="https://www.w3.org/TR/css-flexbox-1/#propdef-flex-basis">
+  <link rel="match" href="flexbox-flex-basis-content-002-ref.html">
+  <link rel="stylesheet" type="text/css" href="support/ahem.css">
+  <style>
+  .container {
+    display: flex;
+    flex-direction: column;
+    justify-content: space-between;
+    border: 2px solid purple;
+    padding: 2px;
+    margin-right: 2em;
+    width: 50px;
+    height: 200px;
+    float: left;
+  }
+
+  .container > * {
+    /* All flex items have "flex-basis: content" (and zero flex-shrink and
+       min-main-size, to avoid any influence from those). */
+    flex-basis: content;
+    flex-shrink: 0;
+    min-height: 0;
+    border: 2px solid teal;
+  }
+
+  .smallText { font: 10px Ahem; }
+  .bigText   { font: 20px Ahem; }
+  .spacerChild::before {
+    content: '';
+    display: block;
+    background: brown;
+    height: 10px;
+    width: 10px;
+  }
+  .justPadding {
+    /* Empty div with 5px padding on each side */
+    padding: 5px;
+    background: cyan;
+  }
+  canvas { background: fuchsia }
+  </style>
+</head>
+<body>
+<!-- Flex items have unspecified size properties: -->
+<div class="container">
+  <div class="smallText">a b</div>
+  <div class="bigText">c</div>
+  <div class="spacerChild"></div>
+  <div class="justPadding"></div>
+  <canvas height="20"></canvas>
+</div>
+
+<!-- Various specified main-size values (should be ignored): -->
+<div class="container">
+  <div class="smallText"    style="height: 0px">a b</div>
+  <div class="bigText"      style="height: 40px">c</div>
+  <div class="spacerChild"  style="height: 20px"></div>
+  <div class="justPadding"  style="height: 10px"></div>
+  <canvas height="20"       style="height: 8px"></canvas>
+</div>
+
+<!-- Various specified cross-size values (should be honored): -->
+<div class="container">
+  <div class="smallText"    style="width: 0px">a b</div>
+  <div class="bigText"      style="width: 40px">c</div>
+  <div class="spacerChild"  style="width: 20px"></div>
+  <div class="justPadding"  style="width: 10px"></div>
+  <canvas height="20"       style="width: 8px"></canvas>
+</div>
+
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-002b.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-002b.html
new file mode 100644
index 0000000000..694e67242e
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-002b.html
@@ -0,0 +1,84 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>
+    CSS Test: Testing "flex-basis: content" (set via the "flex" shorthand)
+    in a column-oriented flex container.
+  </title>
+  <meta charset="utf-8">
+  <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+  <link rel="help" href="https://www.w3.org/TR/css-flexbox-1/#propdef-flex-basis">
+  <link rel="match" href="flexbox-flex-basis-content-002-ref.html">
+  <link rel="stylesheet" type="text/css" href="support/ahem.css">
+  <style>
+  .container {
+    display: flex;
+    flex-direction: column;
+    justify-content: space-between;
+    border: 2px solid purple;
+    padding: 2px;
+    margin-right: 2em;
+    width: 50px;
+    height: 200px;
+    float: left;
+  }
+
+  .container > * {
+    /* All flex items have "flex-basis: content" (and zero flex-shrink and
+       min-main-size, to avoid any influence from those). */
+    flex: 0 0 content;
+    min-height: 0;
+    border: 2px solid teal;
+  }
+
+  .smallText { font: 10px Ahem; }
+  .bigText   { font: 20px Ahem; }
+  .spacerChild::before {
+    content: '';
+    display: block;
+    background: brown;
+    height: 10px;
+    width: 10px;
+  }
+  .justPadding {
+    /* Empty div with 5px padding on each side */
+    padding: 5px;
+    background: cyan;
+  }
+  canvas { background: fuchsia }
+  </style>
+</head>
+<body>
+<!-- Flex items have unspecified size properties: -->
+<div class="container">
+  <div class="smallText">a b</div>
+  <div class="bigText">c</div>
+  <div class="spacerChild"></div>
+  <div class="justPadding"></div>
+  <canvas height="20"></canvas>
+</div>
+
+<!-- Various specified main-size values (should be ignored): -->
+<div class="container">
+  <div class="smallText"    style="height: 0px">a b</div>
+  <div class="bigText"      style="height: 40px">c</div>
+  <div class="spacerChild"  style="height: 20px"></div>
+  <div class="justPadding"  style="height: 10px"></div>
+  <canvas height="20"       style="height: 8px"></canvas>
+</div>
+
+<!-- Various specified cross-size values (should be honored): -->
+<div class="container">
+  <div class="smallText"    style="width: 0px">a b</div>
+  <div class="bigText"      style="width: 40px">c</div>
+  <div class="spacerChild"  style="width: 20px"></div>
+  <div class="justPadding"  style="width: 10px"></div>
+  <canvas height="20"       style="width: 8px"></canvas>
+</div>
+
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-003-ref.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-003-ref.html
new file mode 100644
index 0000000000..63ce9d7429
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-003-ref.html
@@ -0,0 +1,103 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>CSS Reftest Reference</title>
+  <meta charset="utf-8">
+  <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+  <style>
+  .container {
+    clear: both; /* In this reference case, we use floats instead of
+                    flex items (see below), so the container just
+                    needs to reset the float state for each example. */
+  }
+
+  .item {
+    border: 2px solid teal;
+    float: left; /* Use floated elements as a reference for (hopefully)
+                    max-content sized flex items in testcase. */
+  }
+  ib {
+    display: inline-block;
+    background: blue;
+    border: 1px solid gray;
+    width: 15px;
+    height: 10px;
+  }
+  float {
+    float: left;
+    background: fuchsia;
+    border: 1px solid gray;
+    width: 15px;
+    height: 10px;
+  }
+  canvas {
+    background: brown;
+    border: 1px solid gray;
+  }
+  .innerFlex {
+    display: flex;
+  }
+  innerItem {
+    background: salmon;
+    border: 1px solid gray;
+    height: 10px;
+    width: 15px;
+    flex: none;
+  }
+  </style>
+</head>
+<body>
+<!-- In testcase, flex item has several inline-blocks
+     (no spaces, to avoid any text-layout dependency): -->
+<div class="container">
+  <div class="item"><ib></ib><ib></ib><ib></ib></div>
+</div>
+
+<!-- In testcase, flex item has several floats: -->
+<div class="container">
+  <div class="item">
+    <float></float>
+    <float></float>
+    <float></float>
+  </div>
+</div>
+
+<!-- In testcase, flex item has several inline replaced elements:
+     (no spaces, to avoid any text-layout dependency): -->
+<div class="container">
+  <div class="item">
+    <canvas width="15" height="10"></canvas
+    ><canvas width="15" height="10"></canvas
+    ><canvas width="15" height="10"></canvas>
+  </div>
+</div>
+
+<!-- In testcase, flex item *is* a replaced element: -->
+<div class="container">
+  <canvas class="item" width="25" height="10"></canvas>
+</div>
+
+<!-- In testcase, flex item is itself a flex container: -->
+<div class="container">
+  <div class="item innerFlex">
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+  </div>
+</div>
+
+<!-- In testcase, flex item is itself a multi-line flex container: -->
+<div class="container">
+  <div class="item innerFlex" style="flex-wrap: wrap">
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+  </div>
+</div>
+
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-003a.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-003a.html
new file mode 100644
index 0000000000..83dbae0868
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-003a.html
@@ -0,0 +1,123 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>
+    CSS Test: Testing that explicit "flex-basis: content" is treated as
+    "max-content" when calculating flex base size
+  </title>
+  <meta charset="utf-8">
+  <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+  <link rel="help" href="https://www.w3.org/TR/css-flexbox-1/#flex-base-size">
+  <link rel="match" href="flexbox-flex-basis-content-003-ref.html">
+  <style>
+  .container {
+    display: flex;
+    /* flex container has an extremely-constrained width (and items will
+       overflow horizontally). This is intentional, as part of stress-testing
+       item sizing. */
+    width: 1px;
+  }
+
+  .item {
+    /* We give all flex items "flex-basis: content".
+       We also give them zero flex-grow, flex-shrink, and min-main-size, so
+       that the flex base size entirely determines the flex item's size. */
+    flex: 0 0 content;
+    min-width: 0;
+    border: 2px solid teal;
+  }
+  ib {
+    display: inline-block;
+    background: blue;
+    border: 1px solid gray;
+    width: 15px;
+    height: 10px;
+  }
+  float {
+    float: left;
+    background: fuchsia;
+    border: 1px solid gray;
+    width: 15px;
+    height: 10px;
+  }
+  canvas {
+    background: brown;
+    border: 1px solid gray;
+  }
+  .innerFlex {
+    display: flex;
+  }
+  innerItem {
+    background: salmon;
+    border: 1px solid gray;
+    height: 10px;
+    width: 15px;
+    flex: none;
+  }
+  </style>
+</head>
+<body>
+<!-- The idea of this test is to be sure the UA is using the "max-content" size
+     (and not e.g. the "fit-content size") when resolving the flex base size
+     inside each flex container.  To differentiate between max-content and
+     other intrinsic size possibilities (min-content/fit-content), we:
+       - use flex items with a large difference between its min-content size &
+       its max-content size (e.g. wrappable content).
+       - use a very small container (to compress the size, if the UA incorrectly
+       allows the size to be influenced by the container size).
+-->
+
+<!-- Flex item has several inline-blocks
+     (no spaces, to avoid any text-layout dependency): -->
+<div class="container">
+  <div class="item"><ib></ib><ib></ib><ib></ib></div>
+</div>
+
+<!-- Flex item has several floats: -->
+<div class="container">
+  <div class="item">
+    <float></float>
+    <float></float>
+    <float></float>
+  </div>
+</div>
+
+<!-- Flex item has several inline replaced elements:
+     (no spaces, to avoid any text-layout dependency): -->
+<div class="container">
+  <div class="item">
+    <canvas width="15" height="10"></canvas
+    ><canvas width="15" height="10"></canvas
+    ><canvas width="15" height="10"></canvas>
+  </div>
+</div>
+
+<!-- Flex item *is* a replaced element: -->
+<div class="container">
+  <canvas class="item" width="25" height="10"></canvas>
+</div>
+
+<!-- Flex item is itself a flex container: -->
+<div class="container">
+  <div class="item innerFlex">
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+  </div>
+</div>
+
+<!-- Flex item is itself a multi-line flex container: -->
+<div class="container">
+  <div class="item innerFlex" style="flex-wrap: wrap">
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+  </div>
+</div>
+
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-003b.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-003b.html
new file mode 100644
index 0000000000..a81403c098
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-003b.html
@@ -0,0 +1,124 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>
+    CSS Test: Testing that used "flex-basis: content" is treated as
+    "max-content" when calculating flex base size
+  </title>
+  <meta charset="utf-8">
+  <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+  <link rel="help" href="https://www.w3.org/TR/css-flexbox-1/#flex-base-size">
+  <link rel="match" href="flexbox-flex-basis-content-003-ref.html">
+  <style>
+  .container {
+    display: flex;
+    /* flex container has an extremely-constrained width (and items will
+       overflow horizontally). This is intentional, as part of stress-testing
+       item sizing. */
+    width: 1px;
+  }
+
+  .item {
+    /* We give all flex items a used "flex-basis" of "content"
+       (from "flex-basis:auto" and default "width:auto").
+       We also give them zero flex-grow, flex-shrink, and min-main-size, so
+       that the flex base size entirely determines the flex item's size. */
+    flex: 0 0 auto;
+    min-width: 0;
+    border: 2px solid teal;
+  }
+  ib {
+    display: inline-block;
+    background: blue;
+    border: 1px solid gray;
+    width: 15px;
+    height: 10px;
+  }
+  float {
+    float: left;
+    background: fuchsia;
+    border: 1px solid gray;
+    width: 15px;
+    height: 10px;
+  }
+  canvas {
+    background: brown;
+    border: 1px solid gray;
+  }
+  .innerFlex {
+    display: flex;
+  }
+  innerItem {
+    background: salmon;
+    border: 1px solid gray;
+    height: 10px;
+    width: 15px;
+    flex: none;
+  }
+  </style>
+</head>
+<body>
+<!-- The idea of this test is to be sure the UA is using the "max-content" size
+     (and not e.g. the "fit-content size") when resolving the flex base size
+     inside each flex container.  To differentiate between max-content and
+     other intrinsic size possibilities (min-content/fit-content), we:
+       - use flex items with a large difference between its min-content size &
+       its max-content size (e.g. wrappable content).
+       - use a very small container (to compress the size, if the UA incorrectly
+       allows the size to be influenced by the container size).
+-->
+
+<!-- Flex item has several inline-blocks
+     (no spaces, to avoid any text-layout dependency): -->
+<div class="container">
+  <div class="item"><ib></ib><ib></ib><ib></ib></div>
+</div>
+
+<!-- Flex item has several floats: -->
+<div class="container">
+  <div class="item">
+    <float></float>
+    <float></float>
+    <float></float>
+  </div>
+</div>
+
+<!-- Flex item has several inline replaced elements:
+     (no spaces, to avoid any text-layout dependency): -->
+<div class="container">
+  <div class="item">
+    <canvas width="15" height="10"></canvas
+    ><canvas width="15" height="10"></canvas
+    ><canvas width="15" height="10"></canvas>
+  </div>
+</div>
+
+<!-- Flex item *is* a replaced element: -->
+<div class="container">
+  <canvas class="item" width="25" height="10"></canvas>
+</div>
+
+<!-- Flex item is itself a flex container: -->
+<div class="container">
+  <div class="item innerFlex">
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+  </div>
+</div>
+
+<!-- Flex item is itself a multi-line flex container: -->
+<div class="container">
+  <div class="item innerFlex" style="flex-wrap: wrap">
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+  </div>
+</div>
+
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-004-ref.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-004-ref.html
new file mode 100644
index 0000000000..7da4de7a5a
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-004-ref.html
@@ -0,0 +1,105 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>CSS Reftest Reference</title>
+  <meta charset="utf-8">
+  <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+  <style>
+  .container {
+    clear: both; /* In this reference case, we use floats instead of
+                    flex items (see below), so the container just
+                    needs to reset the float state for each example. */
+    height: 50px;
+  }
+
+  .item {
+    border: 2px solid teal;
+    float: left; /* Use floated elements as a reference for (hopefully)
+                    max-content sized flex items in testcase. */
+  }
+  ib {
+    display: inline-block;
+    background: blue;
+    border: 1px solid gray;
+    width: 15px;
+    height: 10px;
+  }
+  float {
+    float: left;
+    background: fuchsia;
+    border: 1px solid gray;
+    width: 15px;
+    height: 10px;
+  }
+  canvas {
+    background: brown;
+    border: 1px solid gray;
+  }
+  .innerFlex {
+    display: flex;
+    flex-direction: column;
+  }
+  innerItem {
+    background: salmon;
+    border: 1px solid gray;
+    height: 10px;
+    width: 15px;
+    flex: none;
+  }
+  </style>
+</head>
+<body>
+<!-- In testcase, flex item has several inline-blocks
+     (no spaces, to avoid any text-layout dependency): -->
+<div class="container">
+  <div class="item"><ib></ib><ib></ib><ib></ib></div>
+</div>
+
+<!-- In testcase, flex item has several floats: -->
+<div class="container">
+  <div class="item">
+    <float></float>
+    <float></float>
+    <float></float>
+  </div>
+</div>
+
+<!-- In testcase, flex item has several inline replaced elements:
+     (no spaces, to avoid any text-layout dependency): -->
+<div class="container">
+  <div class="item">
+    <canvas width="15" height="10"></canvas
+    ><canvas width="15" height="10"></canvas
+    ><canvas width="15" height="10"></canvas>
+  </div>
+</div>
+
+<!-- In testcase, flex item *is* a replaced element: -->
+<div class="container">
+  <canvas class="item" width="25" height="10"></canvas>
+</div>
+
+<!-- In testcase, flex item is itself a flex container: -->
+<div class="container">
+  <div class="item innerFlex">
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+  </div>
+</div>
+
+<!-- In testcase, flex item is itself a multi-line flex container: -->
+<div class="container">
+  <div class="item innerFlex" style="flex-wrap: wrap">
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+  </div>
+</div>
+
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-004a.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-004a.html
new file mode 100644
index 0000000000..65a86b508f
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-004a.html
@@ -0,0 +1,129 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>
+    CSS Test: Testing that explicit "flex-basis: content" is treated as
+    "max-content" when calculating flex base size
+  </title>
+  <meta charset="utf-8">
+  <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+  <link rel="help" href="https://www.w3.org/TR/css-flexbox-1/#flex-base-size">
+  <link rel="match" href="flexbox-flex-basis-content-004-ref.html">
+  <style>
+  .container {
+    display: flex;
+    flex-direction: column;
+    align-items: flex-start;
+    /* flex container has an extremely-constrained height (and items will
+       overflow vertically). This is intentional, as part of stress-testing
+       item sizing. We add a large margin-bottom so that overflowing
+       items don't overlap between examples. */
+    height: 1px;
+    margin-bottom: 49px;
+  }
+
+  .item {
+    /* We give all flex items "flex-basis: content".
+       We also give them zero flex-grow, flex-shrink, and min-main-size, so
+       that the flex base size entirely determines the flex item's size. */
+    flex: 0 0 content;
+    min-height: 0;
+    border: 2px solid teal;
+  }
+  ib {
+    display: inline-block;
+    background: blue;
+    border: 1px solid gray;
+    width: 15px;
+    height: 10px;
+  }
+  float {
+    float: left;
+    background: fuchsia;
+    border: 1px solid gray;
+    width: 15px;
+    height: 10px;
+  }
+  canvas {
+    background: brown;
+    border: 1px solid gray;
+  }
+  .innerFlex {
+    display: flex;
+    flex-direction: column;
+  }
+  innerItem {
+    background: salmon;
+    border: 1px solid gray;
+    height: 10px;
+    width: 15px;
+    flex: none;
+  }
+  </style>
+</head>
+<body>
+<!-- This test exists for symmetry with the previous set of tests
+     (flexbox-flex-basis-content-003*). Those previous tests check how
+     "flex-basis:content" is resolved to a flex base size, in the inline axis,
+     when the container's size is constrained in that axis. This test does the
+     same, but for the *block* axis, using flex-direction:column. As with the
+     previous set of tests, the expectation here is that we should use the
+     item's max-content size as its flex base size. Note that there's a bit
+     less subtlety here because intrinsic sizes (min-content, max-content) are
+     typically all the same in the block axis.
+-->
+
+<!-- Flex item has several inline-blocks
+     (no spaces, to avoid any text-layout dependency): -->
+<div class="container">
+  <div class="item"><ib></ib><ib></ib><ib></ib></div>
+</div>
+
+<!-- Flex item has several floats: -->
+<div class="container">
+  <div class="item">
+    <float></float>
+    <float></float>
+    <float></float>
+  </div>
+</div>
+
+<!-- Flex item has several inline replaced elements:
+     (no spaces, to avoid any text-layout dependency): -->
+<div class="container">
+  <div class="item">
+    <canvas width="15" height="10"></canvas
+    ><canvas width="15" height="10"></canvas
+    ><canvas width="15" height="10"></canvas>
+  </div>
+</div>
+
+<!-- Flex item *is* a replaced element: -->
+<div class="container">
+  <canvas class="item" width="25" height="10"></canvas>
+</div>
+
+<!-- Flex item is itself a flex container: -->
+<div class="container">
+  <div class="item innerFlex">
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+  </div>
+</div>
+
+<!-- Flex item is itself a multi-line flex container: -->
+<div class="container">
+  <div class="item innerFlex" style="flex-wrap: wrap">
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+  </div>
+</div>
+
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-004b.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-004b.html
new file mode 100644
index 0000000000..a686f1aa1e
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-flex-basis-content-004b.html
@@ -0,0 +1,130 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>
+    CSS Test: Testing that used "flex-basis: content" is treated as
+    "max-content" when calculating flex base size
+  </title>
+  <meta charset="utf-8">
+  <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+  <link rel="help" href="https://www.w3.org/TR/css-flexbox-1/#flex-base-size">
+  <link rel="match" href="flexbox-flex-basis-content-004-ref.html">
+  <style>
+  .container {
+    display: flex;
+    flex-direction: column;
+    align-items: flex-start;
+    /* flex container has an extremely-constrained height (and items will
+       overflow vertically). This is intentional, as part of stress-testing
+       item sizing. We add a large margin-bottom so that overflowing
+       items don't overlap between examples. */
+    height: 1px;
+    margin-bottom: 49px;
+  }
+
+  .item {
+    /* We give all flex items a used "flex-basis" of "content"
+       (from "flex-basis:auto" and default "width:auto").
+       We also give them zero flex-grow, flex-shrink, and min-main-size, so
+       that the flex base size entirely determines the flex item's size. */
+    flex: 0 0 auto;
+    min-height: 0;
+    border: 2px solid teal;
+  }
+  ib {
+    display: inline-block;
+    background: blue;
+    border: 1px solid gray;
+    width: 15px;
+    height: 10px;
+  }
+  float {
+    float: left;
+    background: fuchsia;
+    border: 1px solid gray;
+    width: 15px;
+    height: 10px;
+  }
+  canvas {
+    background: brown;
+    border: 1px solid gray;
+  }
+  .innerFlex {
+    display: flex;
+    flex-direction: column;
+  }
+  innerItem {
+    background: salmon;
+    border: 1px solid gray;
+    height: 10px;
+    width: 15px;
+    flex: none;
+  }
+  </style>
+</head>
+<body>
+<!-- This test exists for symmetry with the previous set of tests
+     (flexbox-flex-basis-content-003*). Those previous tests check how
+     "flex-basis:content" is resolved to a flex base size, in the inline axis,
+     when the container's size is constrained in that axis. This test does the
+     same, but for the *block* axis, using flex-direction:column. As with the
+     previous set of tests, the expectation here is that we should use the
+     item's max-content size as its flex base size. Note that there's a bit
+     less subtlety here because intrinsic sizes (min-content, max-content) are
+     typically all the same in the block axis.
+-->
+
+<!-- Flex item has several inline-blocks
+     (no spaces, to avoid any text-layout dependency): -->
+<div class="container">
+  <div class="item"><ib></ib><ib></ib><ib></ib></div>
+</div>
+
+<!-- Flex item has several floats: -->
+<div class="container">
+  <div class="item">
+    <float></float>
+    <float></float>
+    <float></float>
+  </div>
+</div>
+
+<!-- Flex item has several inline replaced elements:
+     (no spaces, to avoid any text-layout dependency): -->
+<div class="container">
+  <div class="item">
+    <canvas width="15" height="10"></canvas
+    ><canvas width="15" height="10"></canvas
+    ><canvas width="15" height="10"></canvas>
+  </div>
+</div>
+
+<!-- Flex item *is* a replaced element: -->
+<div class="container">
+  <canvas class="item" width="25" height="10"></canvas>
+</div>
+
+<!-- Flex item is itself a flex container: -->
+<div class="container">
+  <div class="item innerFlex">
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+  </div>
+</div>
+
+<!-- Flex item is itself a multi-line flex container: -->
+<div class="container">
+  <div class="item innerFlex" style="flex-wrap: wrap">
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+    <innerItem></innerItem>
+  </div>
+</div>
+
+</body>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-gap-position-absolute-ref.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-gap-position-absolute-ref.html
new file mode 100644
index 0000000000..7cea1fb1dd
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-gap-position-absolute-ref.html
@@ -0,0 +1,20 @@
+<!DOCTYPE html>
+<html>
+  <meta charset="utf-8">
+  <title>CSS Flexible Box Layout Test Reference: Test flexbox intrinsic inline-size, gap, and absolute-positioned children</title>
+  <link rel="author" title="Ting-Yu Lin" href="mailto:tlin@mozilla.com">
+  <link rel="author" title="Mozilla" href="http://www.mozilla.org/">
+
+  <style>
+  div {
+    display: inline-flex;
+    background: fuchsia;
+  }
+  </style>
+
+  <div>
+    <span>B</span>
+    <span style="width: 100px;"></span>
+    <span>C</span>
+  </div>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/flexbox-gap-position-absolute.html b/layout/reftests/w3c-css/submitted/flexbox/flexbox-gap-position-absolute.html
new file mode 100644
index 0000000000..850f1a42d4
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/flexbox-gap-position-absolute.html
@@ -0,0 +1,26 @@
+<!DOCTYPE html>
+<html>
+  <meta charset="utf-8">
+  <title>CSS Flexible Box Layout Test: Test flexbox intrinsic inline-size, gap, and absolute-positioned children</title>
+  <link rel="author" title="Ting-Yu Lin" href="mailto:tlin@mozilla.com">
+  <link rel="author" title="Mozilla" href="http://www.mozilla.org/">
+  <link rel="help" href="https://drafts.csswg.org/css-flexbox-1/#intrinsic-sizes">
+  <link rel="help" href="https://drafts.csswg.org/css-align-3/#gaps">
+  <link rel="match" href="flexbox-gap-position-absolute-ref.html">
+  <meta name="assert" content="This test verifies the absolute-positioned children do not contribute the gap size to the flexbox's intrinsic inline-size.">
+
+  <style>
+  div {
+    display: inline-flex;
+    gap: 100px;
+    background: fuchsia;
+  }
+  </style>
+
+  <div>
+    <span style="position: absolute;"></span>
+    <span style="position: fixed;"></span>
+    <span>B</span>
+    <span>C</span>
+  </div>
+</html>
diff --git a/layout/reftests/w3c-css/submitted/flexbox/reftest.list b/layout/reftests/w3c-css/submitted/flexbox/reftest.list
index 281ef4758f..7cac455ae0 100644
--- a/layout/reftests/w3c-css/submitted/flexbox/reftest.list
+++ b/layout/reftests/w3c-css/submitted/flexbox/reftest.list
@@ -91,6 +91,23 @@
 == flexbox-collapsed-item-horiz-002.html flexbox-collapsed-item-horiz-002-ref.html
 == flexbox-collapsed-item-horiz-003.html flexbox-collapsed-item-horiz-003-ref.html
 
+# Tests for "row gap" and "column gap"
+== flexbox-column-row-gap-001.html flexbox-column-row-gap-001-ref.html
+== flexbox-column-row-gap-002.html flexbox-column-row-gap-002-ref.html
+== flexbox-column-row-gap-003.html flexbox-column-row-gap-003-ref.html
+== flexbox-column-row-gap-004.html flexbox-column-row-gap-004-ref.html
+== flexbox-gap-position-absolute.html flexbox-gap-position-absolute-ref.html
+
+# Tests for "flex-basis: content"
+== flexbox-flex-basis-content-001a.html flexbox-flex-basis-content-001-ref.html
+== flexbox-flex-basis-content-001b.html flexbox-flex-basis-content-001-ref.html
+== flexbox-flex-basis-content-002a.html flexbox-flex-basis-content-002-ref.html
+== flexbox-flex-basis-content-002b.html flexbox-flex-basis-content-002-ref.html
+== flexbox-flex-basis-content-003a.html flexbox-flex-basis-content-003-ref.html
+== flexbox-flex-basis-content-003b.html flexbox-flex-basis-content-003-ref.html
+== flexbox-flex-basis-content-004a.html flexbox-flex-basis-content-004-ref.html
+== flexbox-flex-basis-content-004b.html flexbox-flex-basis-content-004-ref.html
+
 # Tests for flex-flow shorthand property
 == flexbox-flex-flow-001.html flexbox-flex-flow-001-ref.html
 == flexbox-flex-flow-002.html flexbox-flex-flow-002-ref.html
diff --git a/layout/style/Declaration.cpp b/layout/style/Declaration.cpp
index 9d7ca312c4..29cae7a3b6 100644
--- a/layout/style/Declaration.cpp
+++ b/layout/style/Declaration.cpp
@@ -1248,18 +1248,6 @@ Declaration::GetPropertyValueInternal(
     // #2 <'grid-template-rows'> / [ auto-flow && dense? ] <'grid-auto-columns'>?
     // #3 [ auto-flow && dense? ] <'grid-auto-rows'>? / <'grid-template-columns'>
     case eCSSProperty_grid: {
-      const nsCSSValue& columnGapValue =
-        *data->ValueFor(eCSSProperty_grid_column_gap);
-      if (columnGapValue.GetUnit() != eCSSUnit_Pixel ||
-          columnGapValue.GetFloatValue() != 0.0f) {
-        return; // Not serializable, bail.
-      }
-      const nsCSSValue& rowGapValue =
-        *data->ValueFor(eCSSProperty_grid_row_gap);
-      if (rowGapValue.GetUnit() != eCSSUnit_Pixel ||
-          rowGapValue.GetFloatValue() != 0.0f) {
-        return; // Not serializable, bail.
-      }
       const nsCSSValue& areasValue =
         *data->ValueFor(eCSSProperty_grid_template_areas);
       const nsCSSValue& columnsValue =
@@ -1475,7 +1463,7 @@ Declaration::GetPropertyValueInternal(
       }
       MOZ_FALLTHROUGH;
     }
-    case eCSSProperty_grid_gap: {
+    case eCSSProperty_gap: {
       const nsCSSPropertyID* subprops =
         nsCSSProps::SubpropertyEntryFor(aProperty);
       MOZ_ASSERT(subprops[2] == eCSSProperty_UNKNOWN,
diff --git a/layout/style/nsCSSKeywordList.h b/layout/style/nsCSSKeywordList.h
index 2629127fae..7e661bc483 100644
--- a/layout/style/nsCSSKeywordList.h
+++ b/layout/style/nsCSSKeywordList.h
@@ -205,6 +205,7 @@ CSS_KEY(column, column)
 CSS_KEY(column-reverse, column_reverse)
 CSS_KEY(condensed, condensed)
 CSS_KEY(contain, contain)
+CSS_KEY(content, content)
 CSS_KEY(content-box, content_box)
 CSS_KEY(contents, contents)
 CSS_KEY(context-fill, context_fill)
diff --git a/layout/style/nsCSSParser.cpp b/layout/style/nsCSSParser.cpp
index 2b0f5ad24a..2e606af05c 100644
--- a/layout/style/nsCSSParser.cpp
+++ b/layout/style/nsCSSParser.cpp
@@ -1015,7 +1015,7 @@ protected:
   bool ParseGridColumnRow(nsCSSPropertyID aStartPropID,
                           nsCSSPropertyID aEndPropID);
   bool ParseGridArea();
-  bool ParseGridGap();
+  bool ParseGap();
 
   bool ParseInitialLetter();
 
@@ -8638,7 +8638,7 @@ CSSParserImpl::ParseFlex()
   // "a unitless zero that is not already preceded by two flex factors must be
   //  interpreted as a flex factor.
   if (ParseNonNegativeVariant(tmpVal, flexBasisVariantMask | VARIANT_NUMBER,
-                              nsCSSProps::kWidthKTable) != CSSParseResult::Ok) {
+                              nsCSSProps::kFlexBasisKTable) != CSSParseResult::Ok) {
     // First component was not a valid flex-basis or flex-grow value. Fail.
     return false;
   }
@@ -8687,7 +8687,7 @@ CSSParserImpl::ParseFlex()
     if (!wasFirstComponentFlexBasis) {
       CSSParseResult result =
         ParseNonNegativeVariant(tmpVal, flexBasisVariantMask,
-                                nsCSSProps::kWidthKTable);
+                                nsCSSProps::kFlexBasisKTable);
       if (result == CSSParseResult::Error) {
         return false;
       } else if (result == CSSParseResult::Ok) {
@@ -9774,13 +9774,6 @@ CSSParserImpl::ParseGrid()
     return true;
   }
 
-  // https://drafts.csswg.org/css-grid/#grid-shorthand
-  // "Also, the gutter properties are reset by this shorthand,
-  //  even though they can't be set by it."
-  value.SetFloatValue(0.0f, eCSSUnit_Pixel);
-  AppendValue(eCSSProperty_grid_row_gap, value);
-  AppendValue(eCSSProperty_grid_column_gap, value);
-
   // [ auto-flow && dense? ] <'grid-auto-rows'>? / <'grid-template-columns'>
   auto res = ParseGridShorthandAutoProps(NS_STYLE_GRID_AUTO_FLOW_ROW);
   if (res == CSSParseResult::Error) {
@@ -10087,12 +10080,12 @@ CSSParserImpl::ParseGridArea()
 }
 
 bool
-CSSParserImpl::ParseGridGap()
+CSSParserImpl::ParseGap()
 {
   nsCSSValue first;
   if (ParseSingleTokenVariant(first, VARIANT_INHERIT, nullptr)) {
-    AppendValue(eCSSProperty_grid_row_gap, first);
-    AppendValue(eCSSProperty_grid_column_gap, first);
+    AppendValue(eCSSProperty_row_gap, first);
+    AppendValue(eCSSProperty_column_gap, first);
     return true;
   }
   if (ParseNonNegativeVariant(first, VARIANT_LPCALC, nullptr) !=
@@ -10104,8 +10097,8 @@ CSSParserImpl::ParseGridGap()
   if (result == CSSParseResult::Error) {
     return false;
   }
-  AppendValue(eCSSProperty_grid_row_gap, first);
-  AppendValue(eCSSProperty_grid_column_gap,
+  AppendValue(eCSSProperty_row_gap, first);
+  AppendValue(eCSSProperty_column_gap,
               result == CSSParseResult::NotFound ? first : second);
   return true;
 }
@@ -12005,8 +11998,8 @@ CSSParserImpl::ParsePropertyByFunction(nsCSSPropertyID aPropID)
                               eCSSProperty_grid_row_end);
   case eCSSProperty_grid_area:
     return ParseGridArea();
-  case eCSSProperty_grid_gap:
-    return ParseGridGap();
+  case eCSSProperty_gap:
+    return ParseGap();
   case eCSSProperty_image_region:
     return ParseRect(eCSSProperty_image_region);
   case eCSSProperty_align_content:
diff --git a/layout/style/nsCSSPropAliasList.h b/layout/style/nsCSSPropAliasList.h
index 4f2a6e6b6d..7043d1931e 100644
--- a/layout/style/nsCSSPropAliasList.h
+++ b/layout/style/nsCSSPropAliasList.h
@@ -34,6 +34,18 @@
 
  ******/
 
+CSS_PROP_ALIAS(grid-gap,
+               gap,
+               GridGap,
+               "")
+CSS_PROP_ALIAS(grid-column-gap,
+               column_gap,
+               GridColumnGap,
+               "")
+CSS_PROP_ALIAS(grid-row-gap,
+               row_gap,
+               GridRowGap,
+               "")
 CSS_PROP_ALIAS(word-wrap,
                overflow_wrap,
                WordWrap,
diff --git a/layout/style/nsCSSPropList.h b/layout/style/nsCSSPropList.h
index 45e919d4f8..ae5de51e5a 100644
--- a/layout/style/nsCSSPropList.h
+++ b/layout/style/nsCSSPropList.h
@@ -1516,7 +1516,7 @@ CSS_PROP_COLUMN(
     kColumnFillKTable,
     CSS_PROP_NO_OFFSET,
     eStyleAnimType_Discrete)
-CSS_PROP_COLUMN(
+CSS_PROP_POSITION(
     column-gap,
     column_gap,
     ColumnGap,
@@ -1525,7 +1525,7 @@ CSS_PROP_COLUMN(
     "",
     VARIANT_HLP | VARIANT_NORMAL | VARIANT_CALC,
     nullptr,
-    offsetof(nsStyleColumn, mColumnGap),
+    offsetof(nsStylePosition, mColumnGap),
     eStyleAnimType_Coord)
 CSS_PROP_SHORTHAND(
     column-rule,
@@ -1758,7 +1758,7 @@ CSS_PROP_POSITION(
     // its own code to parse each subproperty. It does not depend on the
     // longhand parsing defined here.
     VARIANT_AHKLP | VARIANT_CALC,
-    kWidthKTable,
+    kFlexBasisKTable,
     offsetof(nsStylePosition, mFlexBasis),
     eStyleAnimType_Coord)
 CSS_PROP_POSITION(
@@ -2099,26 +2099,31 @@ CSS_PROP_UIRESET(
     nullptr,
     CSS_PROP_NO_OFFSET,
     eStyleAnimType_Discrete) // bug 58646
+CSS_PROP_SHORTHAND(
+    gap,
+    gap,
+    Gap,
+    CSS_PROPERTY_PARSE_FUNCTION,
+    "")
 CSS_PROP_SHORTHAND(
     grid,
     grid,
     Grid,
     CSS_PROPERTY_PARSE_FUNCTION,
-    "layout.css.grid.enabled")
+    "")
 CSS_PROP_SHORTHAND(
     grid-area,
     grid_area,
     GridArea,
     CSS_PROPERTY_PARSE_FUNCTION,
-    "layout.css.grid.enabled")
+    "")
 CSS_PROP_POSITION(
     grid-auto-columns,
     grid_auto_columns,
     GridAutoColumns,
     CSS_PROPERTY_PARSE_FUNCTION |
-        CSS_PROPERTY_STORES_CALC |
-        CSS_PROPERTY_ENABLED_IN_UA_SHEETS,
-    "layout.css.grid.enabled",
+        CSS_PROPERTY_STORES_CALC,
+    "",
     0,
     kGridTrackBreadthKTable,
     CSS_PROP_NO_OFFSET,
@@ -2127,9 +2132,8 @@ CSS_PROP_POSITION(
     grid-auto-flow,
     grid_auto_flow,
     GridAutoFlow,
-    CSS_PROPERTY_PARSE_FUNCTION |
-        CSS_PROPERTY_ENABLED_IN_UA_SHEETS,
-    "layout.css.grid.enabled",
+    CSS_PROPERTY_PARSE_FUNCTION,
+    "",
     0,
     kGridAutoFlowKTable,
     CSS_PROP_NO_OFFSET,
@@ -2139,9 +2143,8 @@ CSS_PROP_POSITION(
     grid_auto_rows,
     GridAutoRows,
     CSS_PROPERTY_PARSE_FUNCTION |
-        CSS_PROPERTY_STORES_CALC |
-        CSS_PROPERTY_ENABLED_IN_UA_SHEETS,
-    "layout.css.grid.enabled",
+        CSS_PROPERTY_STORES_CALC,
+    "",
     0,
     kGridTrackBreadthKTable,
     CSS_PROP_NO_OFFSET,
@@ -2151,79 +2154,49 @@ CSS_PROP_SHORTHAND(
     grid_column,
     GridColumn,
     CSS_PROPERTY_PARSE_FUNCTION,
-    "layout.css.grid.enabled")
+    "")
 CSS_PROP_POSITION(
     grid-column-end,
     grid_column_end,
     GridColumnEnd,
     CSS_PROPERTY_PARSE_FUNCTION,
-    "layout.css.grid.enabled",
+    "",
     0,
     nullptr,
     CSS_PROP_NO_OFFSET,
     eStyleAnimType_Discrete)
-CSS_PROP_POSITION(
-    grid-column-gap,
-    grid_column_gap,
-    GridColumnGap,
-    CSS_PROPERTY_PARSE_VALUE |
-        CSS_PROPERTY_VALUE_NONNEGATIVE |
-        CSS_PROPERTY_ENABLED_IN_UA_SHEETS,
-    "layout.css.grid.enabled",
-    VARIANT_HLP | VARIANT_CALC,
-    nullptr,
-    offsetof(nsStylePosition, mGridColumnGap),
-    eStyleAnimType_Coord)
 CSS_PROP_POSITION(
     grid-column-start,
     grid_column_start,
     GridColumnStart,
     CSS_PROPERTY_PARSE_FUNCTION,
-    "layout.css.grid.enabled",
+    "",
     0,
     nullptr,
     CSS_PROP_NO_OFFSET,
     eStyleAnimType_Discrete)
-CSS_PROP_SHORTHAND(
-    grid-gap,
-    grid_gap,
-    GridGap,
-    CSS_PROPERTY_PARSE_FUNCTION,
-    "layout.css.grid.enabled")
 CSS_PROP_SHORTHAND(
     grid-row,
     grid_row,
     GridRow,
     CSS_PROPERTY_PARSE_FUNCTION,
-    "layout.css.grid.enabled")
+    "")
 CSS_PROP_POSITION(
     grid-row-end,
     grid_row_end,
     GridRowEnd,
     CSS_PROPERTY_PARSE_FUNCTION,
-    "layout.css.grid.enabled",
+    "",
     0,
     nullptr,
     CSS_PROP_NO_OFFSET,
     eStyleAnimType_Discrete)
-CSS_PROP_POSITION(
-    grid-row-gap,
-    grid_row_gap,
-    GridRowGap,
-    CSS_PROPERTY_PARSE_VALUE |
-        CSS_PROPERTY_VALUE_NONNEGATIVE |
-        CSS_PROPERTY_ENABLED_IN_UA_SHEETS,
-    "layout.css.grid.enabled",
-    VARIANT_HLP | VARIANT_CALC,
-    nullptr,
-    offsetof(nsStylePosition, mGridRowGap),
-    eStyleAnimType_Coord)
 CSS_PROP_POSITION(
     grid-row-start,
     grid_row_start,
     GridRowStart,
     CSS_PROPERTY_PARSE_FUNCTION,
-    "layout.css.grid.enabled",
+    "",
     0,
     nullptr,
     CSS_PROP_NO_OFFSET,
@@ -2233,14 +2206,13 @@ CSS_PROP_SHORTHAND(
     grid_template,
     GridTemplate,
     CSS_PROPERTY_PARSE_FUNCTION,
-    "layout.css.grid.enabled")
+    "")
 CSS_PROP_POSITION(
     grid-template-areas,
     grid_template_areas,
     GridTemplateAreas,
-    CSS_PROPERTY_PARSE_FUNCTION |
-        CSS_PROPERTY_ENABLED_IN_UA_SHEETS,
-    "layout.css.grid.enabled",
+    CSS_PROPERTY_PARSE_FUNCTION,
+    "",
     0,
     nullptr,
     CSS_PROP_NO_OFFSET,
@@ -2251,9 +2223,8 @@ CSS_PROP_POSITION(
     GridTemplateColumns,
     CSS_PROPERTY_PARSE_FUNCTION |
         CSS_PROPERTY_STORES_CALC |
-        CSS_PROPERTY_GETCS_NEEDS_LAYOUT_FLUSH |
-        CSS_PROPERTY_ENABLED_IN_UA_SHEETS,
-    "layout.css.grid.enabled",
+        CSS_PROPERTY_GETCS_NEEDS_LAYOUT_FLUSH,
+    "",
     0,
     kGridTrackBreadthKTable,
     CSS_PROP_NO_OFFSET,
@@ -2264,9 +2235,8 @@ CSS_PROP_POSITION(
     GridTemplateRows,
     CSS_PROPERTY_PARSE_FUNCTION |
         CSS_PROPERTY_STORES_CALC |
-        CSS_PROPERTY_GETCS_NEEDS_LAYOUT_FLUSH |
-        CSS_PROPERTY_ENABLED_IN_UA_SHEETS,
-    "layout.css.grid.enabled",
+        CSS_PROPERTY_GETCS_NEEDS_LAYOUT_FLUSH,
+    "",
     0,
     kGridTrackBreadthKTable,
     CSS_PROP_NO_OFFSET,
@@ -3560,6 +3530,17 @@ CSS_PROP_POSITION(
     nullptr,
     offsetof(nsStylePosition, mOffset),
     eStyleAnimType_Sides_Right)
+CSS_PROP_POSITION(
+    row-gap,
+    row_gap,
+    RowGap,
+    CSS_PROPERTY_PARSE_VALUE |
+        CSS_PROPERTY_VALUE_NONNEGATIVE,
+    "",
+    VARIANT_HLP | VARIANT_NORMAL | VARIANT_CALC,
+    nullptr,
+    offsetof(nsStylePosition, mRowGap),
+    eStyleAnimType_Coord)
 CSS_PROP_TEXT(
     ruby-align,
     ruby_align,
diff --git a/layout/style/nsCSSProps.cpp b/layout/style/nsCSSProps.cpp
index 461b3e3ee3..d33878ecdf 100644
--- a/layout/style/nsCSSProps.cpp
+++ b/layout/style/nsCSSProps.cpp
@@ -1334,7 +1334,6 @@ KTableEntry nsCSSProps::kDisplayKTable[] = {
   { eCSSKeyword_ruby_base_container, StyleDisplay::RubyBaseContainer },
   { eCSSKeyword_ruby_text,           StyleDisplay::RubyText },
   { eCSSKeyword_ruby_text_container, StyleDisplay::RubyTextContainer },
-  // The next two entries are controlled by the layout.css.grid.enabled pref.
   { eCSSKeyword_grid,                StyleDisplay::Grid },
   { eCSSKeyword_inline_grid,         StyleDisplay::InlineGrid },
   // The next 4 entries are controlled by the layout.css.prefixes.webkit pref.
@@ -2264,6 +2263,20 @@ const KTableEntry nsCSSProps::kWidthKTable[] = {
   { eCSSKeyword_UNKNOWN, -1 }
 };
 
+// This must be the same as kWidthKTable, but just with 'content' added:
+const KTableEntry nsCSSProps::kFlexBasisKTable[] = {
+  { eCSSKeyword__moz_max_content, NS_STYLE_WIDTH_MAX_CONTENT },
+  { eCSSKeyword__moz_min_content, NS_STYLE_WIDTH_MIN_CONTENT },
+  { eCSSKeyword__moz_fit_content, NS_STYLE_WIDTH_FIT_CONTENT },
+  { eCSSKeyword__moz_available,   NS_STYLE_WIDTH_AVAILABLE },
+  { eCSSKeyword_content,          NS_STYLE_FLEX_BASIS_CONTENT },
+  { eCSSKeyword_UNKNOWN, -1 }
+};
+static_assert(ArrayLength(nsCSSProps::kFlexBasisKTable) ==
+              ArrayLength(nsCSSProps::kWidthKTable) + 1,
+              "kFlexBasisKTable should have the same entries as "
+              "kWidthKTable, plus one more for 'content'");
+
 const KTableEntry nsCSSProps::kWindowDraggingKTable[] = {
   { eCSSKeyword_default, StyleWindowDragging::Default },
   { eCSSKeyword_drag, StyleWindowDragging::Drag },
@@ -2955,8 +2968,6 @@ static const nsCSSPropertyID gGridSubpropTable[] = {
   eCSSProperty_grid_auto_flow,
   eCSSProperty_grid_auto_rows,
   eCSSProperty_grid_auto_columns,
-  eCSSProperty_grid_row_gap, // can only be reset, not get/set
-  eCSSProperty_grid_column_gap, // can only be reset, not get/set
   eCSSProperty_UNKNOWN
 };
 
@@ -2980,9 +2991,9 @@ static const nsCSSPropertyID gGridAreaSubpropTable[] = {
   eCSSProperty_UNKNOWN
 };
 
-static const nsCSSPropertyID gGridGapSubpropTable[] = {
-  eCSSProperty_grid_row_gap,
-  eCSSProperty_grid_column_gap,
+static const nsCSSPropertyID gGapSubpropTable[] = {
+  eCSSProperty_row_gap,
+  eCSSProperty_column_gap,
   eCSSProperty_UNKNOWN
 };
 
diff --git a/layout/style/nsCSSProps.h b/layout/style/nsCSSProps.h
index 7b8c56860c..cf7ffda78f 100644
--- a/layout/style/nsCSSProps.h
+++ b/layout/style/nsCSSProps.h
@@ -892,6 +892,7 @@ public:
   static const KTableEntry kVolumeKTable[];
   static const KTableEntry kWhitespaceKTable[];
   static const KTableEntry kWidthKTable[]; // also min-width, max-width
+  static const KTableEntry kFlexBasisKTable[];
   static const KTableEntry kWindowDraggingKTable[];
   static const KTableEntry kWindowShadowKTable[];
   static const KTableEntry kWordBreakKTable[];
diff --git a/layout/style/nsComputedDOMStyle.cpp b/layout/style/nsComputedDOMStyle.cpp
index efa485f613..b3c4ccc148 100644
--- a/layout/style/nsComputedDOMStyle.cpp
+++ b/layout/style/nsComputedDOMStyle.cpp
@@ -1092,21 +1092,6 @@ nsComputedDOMStyle::DoGetColumnWidth()
   return val.forget();
 }
 
-already_AddRefed<CSSValue>
-nsComputedDOMStyle::DoGetColumnGap()
-{
-  RefPtr<nsROCSSPrimitiveValue> val = new nsROCSSPrimitiveValue;
-
-  const nsStyleColumn* column = StyleColumn();
-  if (column->mColumnGap.GetUnit() == eStyleUnit_Normal) {
-    val->SetAppUnits(StyleFont()->mFont.size);
-  } else {
-    SetValueToCoord(val, StyleColumn()->mColumnGap, true);
-  }
-
-  return val.forget();
-}
-
 already_AddRefed<CSSValue>
 nsComputedDOMStyle::DoGetColumnFill()
 {
@@ -3003,18 +2988,32 @@ nsComputedDOMStyle::DoGetGridRowEnd()
 }
 
 already_AddRefed<CSSValue>
-nsComputedDOMStyle::DoGetGridColumnGap()
+nsComputedDOMStyle::DoGetColumnGap()
 {
   RefPtr<nsROCSSPrimitiveValue> val = new nsROCSSPrimitiveValue;
-  SetValueToCoord(val, StylePosition()->mGridColumnGap, true);
+
+  const nsStylePosition* positionData = StylePosition();
+  if (positionData->mColumnGap.GetUnit() == eStyleUnit_Normal) {
+    val->SetIdent(eCSSKeyword_normal);
+  } else {
+    SetValueToCoord(val, positionData->mColumnGap, true);
+  }
+
   return val.forget();
 }
 
 already_AddRefed<CSSValue>
-nsComputedDOMStyle::DoGetGridRowGap()
+nsComputedDOMStyle::DoGetRowGap()
 {
   RefPtr<nsROCSSPrimitiveValue> val = new nsROCSSPrimitiveValue;
-  SetValueToCoord(val, StylePosition()->mGridRowGap, true);
+
+  const nsStylePosition* positionData = StylePosition();
+  if (positionData->mRowGap.GetUnit() == eStyleUnit_Normal) {
+    val->SetIdent(eCSSKeyword_normal);
+  } else {
+    SetValueToCoord(val, positionData->mRowGap, true);
+  }
+
   return val.forget();
 }
 
@@ -4425,7 +4424,7 @@ nsComputedDOMStyle::DoGetFlexBasis()
   //   }
 
   SetValueToCoord(val, StylePosition()->mFlexBasis, true,
-                  nullptr, nsCSSProps::kWidthKTable);
+                  nullptr, nsCSSProps::kFlexBasisKTable);
   return val.forget();
 }
 
diff --git a/layout/style/nsComputedDOMStyle.h b/layout/style/nsComputedDOMStyle.h
index 38a61e23c5..363de2a8fe 100644
--- a/layout/style/nsComputedDOMStyle.h
+++ b/layout/style/nsComputedDOMStyle.h
@@ -286,8 +286,6 @@ private:
   already_AddRefed<CSSValue> DoGetGridColumnEnd();
   already_AddRefed<CSSValue> DoGetGridRowStart();
   already_AddRefed<CSSValue> DoGetGridRowEnd();
-  already_AddRefed<CSSValue> DoGetGridColumnGap();
-  already_AddRefed<CSSValue> DoGetGridRowGap();
 
   /* StyleImageLayer properties */
   already_AddRefed<CSSValue> DoGetImageLayerImage(const nsStyleImageLayers& aLayers);
@@ -503,7 +501,6 @@ private:
   already_AddRefed<CSSValue> DoGetColumnCount();
   already_AddRefed<CSSValue> DoGetColumnFill();
   already_AddRefed<CSSValue> DoGetColumnWidth();
-  already_AddRefed<CSSValue> DoGetColumnGap();
   already_AddRefed<CSSValue> DoGetColumnRuleWidth();
   already_AddRefed<CSSValue> DoGetColumnRuleStyle();
   already_AddRefed<CSSValue> DoGetColumnRuleColor();
@@ -541,6 +538,8 @@ private:
   already_AddRefed<CSSValue> DoGetJustifyContent();
   already_AddRefed<CSSValue> DoGetJustifyItems();
   already_AddRefed<CSSValue> DoGetJustifySelf();
+  already_AddRefed<CSSValue> DoGetColumnGap();
+  already_AddRefed<CSSValue> DoGetRowGap();
 
   /* SVG properties */
   already_AddRefed<CSSValue> DoGetFill();
diff --git a/layout/style/nsComputedDOMStylePropertyList.h b/layout/style/nsComputedDOMStylePropertyList.h
index ec223cda4c..a17a6a8223 100644
--- a/layout/style/nsComputedDOMStylePropertyList.h
+++ b/layout/style/nsComputedDOMStylePropertyList.h
@@ -151,10 +151,8 @@ COMPUTED_STYLE_PROP(grid_auto_columns,             GridAutoColumns)
 COMPUTED_STYLE_PROP(grid_auto_flow,                GridAutoFlow)
 COMPUTED_STYLE_PROP(grid_auto_rows,                GridAutoRows)
 COMPUTED_STYLE_PROP(grid_column_end,               GridColumnEnd)
-COMPUTED_STYLE_PROP(grid_column_gap,               GridColumnGap)
 COMPUTED_STYLE_PROP(grid_column_start,             GridColumnStart)
 COMPUTED_STYLE_PROP(grid_row_end,                  GridRowEnd)
-COMPUTED_STYLE_PROP(grid_row_gap,                  GridRowGap)
 COMPUTED_STYLE_PROP(grid_row_start,                GridRowStart)
 COMPUTED_STYLE_PROP(grid_template_areas,           GridTemplateAreas)
 COMPUTED_STYLE_PROP(grid_template_columns,         GridTemplateColumns)
@@ -217,6 +215,7 @@ COMPUTED_STYLE_PROP(position,                      Position)
 COMPUTED_STYLE_PROP(quotes,                        Quotes)
 COMPUTED_STYLE_PROP(resize,                        Resize)
 COMPUTED_STYLE_PROP(right,                         Right)
+COMPUTED_STYLE_PROP(row_gap,                       RowGap)
 COMPUTED_STYLE_PROP(ruby_align,                    RubyAlign)
 COMPUTED_STYLE_PROP(ruby_position,                 RubyPosition)
 COMPUTED_STYLE_PROP(scroll_behavior,               ScrollBehavior)
diff --git a/layout/style/nsLayoutStylesheetCache.cpp b/layout/style/nsLayoutStylesheetCache.cpp
index 1905d8c5cd..7c09202e6a 100644
--- a/layout/style/nsLayoutStylesheetCache.cpp
+++ b/layout/style/nsLayoutStylesheetCache.cpp
@@ -379,8 +379,6 @@ nsLayoutStylesheetCache::For(StyleBackendType aType)
     // style sheets will be re-parsed.
     // Preferences::RegisterCallback(&DependentPrefChanged,
     //                               "layout.css.example-pref.enabled");
-    Preferences::RegisterCallback(&DependentPrefChanged,
-                                  "layout.css.grid.enabled");
     Preferences::RegisterCallback(&DependentPrefChanged,
                                   "dom.details_element.enabled");
   }
@@ -553,7 +551,7 @@ nsLayoutStylesheetCache::DependentPrefChanged(const char* aPref, void* aData)
   InvalidateSheet(gStyleCache_Gecko ? &gStyleCache_Gecko->sheet_ : nullptr, \
                   gStyleCache_Servo ? &gStyleCache_Servo->sheet_ : nullptr);
 
-  INVALIDATE(mUASheet);  // for layout.css.grid.enabled
+  // INVALIDATE(mUASheet);  // for layout.css.example-pref.enabled
   INVALIDATE(mHTMLSheet); // for dom.details_element.enabled
 
 #undef INVALIDATE
diff --git a/layout/style/nsRuleNode.cpp b/layout/style/nsRuleNode.cpp
index 9d0821406b..c8ec5a6b57 100644
--- a/layout/style/nsRuleNode.cpp
+++ b/layout/style/nsRuleNode.cpp
@@ -8877,25 +8877,27 @@ nsRuleNode::ComputePositionData(void* aStartStruct,
               parentPos->mGridRowEnd,
               conditions);
 
-  // grid-column-gap
-  if (SetCoord(*aRuleData->ValueForGridColumnGap(),
-               pos->mGridColumnGap, parentPos->mGridColumnGap,
-               SETCOORD_LPH | SETCOORD_INITIAL_ZERO | SETCOORD_STORE_CALC |
-               SETCOORD_CALC_CLAMP_NONNEGATIVE | SETCOORD_UNSET_INITIAL,
+  // column-gap: normal, length, percent, calc, inherit, initial
+  if (SetCoord(*aRuleData->ValueForColumnGap(),
+               pos->mColumnGap, parentPos->mColumnGap,
+               SETCOORD_LPH | SETCOORD_NORMAL | SETCOORD_INITIAL_NORMAL |
+               SETCOORD_STORE_CALC | SETCOORD_CALC_CLAMP_NONNEGATIVE |
+               SETCOORD_UNSET_INITIAL,
                aContext, mPresContext, conditions)) {
   } else {
-    MOZ_ASSERT(aRuleData->ValueForGridColumnGap()->GetUnit() == eCSSUnit_Null,
+    MOZ_ASSERT(aRuleData->ValueForColumnGap()->GetUnit() == eCSSUnit_Null,
                "unexpected unit");
   }
 
-  // grid-row-gap
-  if (SetCoord(*aRuleData->ValueForGridRowGap(),
-               pos->mGridRowGap, parentPos->mGridRowGap,
-               SETCOORD_LPH | SETCOORD_INITIAL_ZERO | SETCOORD_STORE_CALC |
-               SETCOORD_CALC_CLAMP_NONNEGATIVE | SETCOORD_UNSET_INITIAL,
+  // row-gap: normal, length, percent, calc, inherit, initial
+  if (SetCoord(*aRuleData->ValueForRowGap(),
+               pos->mRowGap, parentPos->mRowGap,
+               SETCOORD_LPH | SETCOORD_NORMAL | SETCOORD_INITIAL_NORMAL |
+               SETCOORD_STORE_CALC | SETCOORD_CALC_CLAMP_NONNEGATIVE |
+               SETCOORD_UNSET_INITIAL,
                aContext, mPresContext, conditions)) {
   } else {
-    MOZ_ASSERT(aRuleData->ValueForGridRowGap()->GetUnit() == eCSSUnit_Null,
+    MOZ_ASSERT(aRuleData->ValueForRowGap()->GetUnit() == eCSSUnit_Null,
                "unexpected unit");
   }
 
@@ -9302,18 +9304,6 @@ nsRuleNode::ComputeColumnData(void* aStartStruct,
              SETCOORD_UNSET_INITIAL,
            aContext, mPresContext, conditions);
 
-  // column-gap: length, inherit, normal
-  SetCoord(*aRuleData->ValueForColumnGap(),
-           column->mColumnGap, parent->mColumnGap,
-           SETCOORD_LH | SETCOORD_NORMAL | SETCOORD_INITIAL_NORMAL |
-             SETCOORD_CALC_LENGTH_ONLY | SETCOORD_UNSET_INITIAL,
-           aContext, mPresContext, conditions);
-  // clamp negative calc() to 0
-  if (column->mColumnGap.GetUnit() == eStyleUnit_Coord) {
-    column->mColumnGap.SetCoordValue(
-      std::max(column->mColumnGap.GetCoordValue(), 0));
-  }
-
   // column-count: auto, integer, inherit
   const nsCSSValue* columnCountValue = aRuleData->ValueForColumnCount();
   if (eCSSUnit_Auto == columnCountValue->GetUnit() ||
diff --git a/layout/style/nsStyleConsts.h b/layout/style/nsStyleConsts.h
index 60377928b0..7f2463733e 100644
--- a/layout/style/nsStyleConsts.h
+++ b/layout/style/nsStyleConsts.h
@@ -778,6 +778,12 @@ enum class StyleDisplay : uint8_t {
 #define NS_STYLE_WIDTH_MIN_CONTENT              1
 #define NS_STYLE_WIDTH_FIT_CONTENT              2
 #define NS_STYLE_WIDTH_AVAILABLE                3
+// The 'content' keyword is only valid for 'flex-basis' (not for 'width').
+// Since the 'flex-basis' property accepts exactly the same values as 'width',
+// this 'flex-basis'-specific enumerated value is listed alongside the
+// 'width' ones, to be sure we don't accidentally overload this numeric
+// value with two different meanings if new 'width' keywords are added.
+#define NS_STYLE_FLEX_BASIS_CONTENT             4
 
 // See nsStyleDisplay.mPosition
 #define NS_STYLE_POSITION_STATIC                0
diff --git a/layout/style/nsStyleStruct.cpp b/layout/style/nsStyleStruct.cpp
index acf287ea8a..e83a6dcf95 100644
--- a/layout/style/nsStyleStruct.cpp
+++ b/layout/style/nsStyleStruct.cpp
@@ -825,7 +825,6 @@ nsStyleXUL::CalcDifference(const nsStyleXUL& aNewData) const
 nsStyleColumn::nsStyleColumn(StyleStructContext aContext)
   : mColumnCount(NS_STYLE_COLUMN_COUNT_AUTO)
   , mColumnWidth(eStyleUnit_Auto)
-  , mColumnGap(eStyleUnit_Normal)
   , mColumnRuleColor(StyleComplexColor::CurrentColor())
   , mColumnRuleStyle(NS_STYLE_BORDER_STYLE_NONE)
   , mColumnFill(NS_STYLE_COLUMN_FILL_BALANCE)
@@ -844,7 +843,6 @@ nsStyleColumn::~nsStyleColumn()
 nsStyleColumn::nsStyleColumn(const nsStyleColumn& aSource)
   : mColumnCount(aSource.mColumnCount)
   , mColumnWidth(aSource.mColumnWidth)
-  , mColumnGap(aSource.mColumnGap)
   , mColumnRuleColor(aSource.mColumnRuleColor)
   , mColumnRuleStyle(aSource.mColumnRuleStyle)
   , mColumnFill(aSource.mColumnFill)
@@ -867,7 +865,6 @@ nsStyleColumn::CalcDifference(const nsStyleColumn& aNewData) const
   }
 
   if (mColumnWidth != aNewData.mColumnWidth ||
-      mColumnGap != aNewData.mColumnGap ||
       mColumnFill != aNewData.mColumnFill) {
     return NS_STYLE_HINT_REFLOW;
   }
@@ -1423,8 +1420,8 @@ nsStylePosition::nsStylePosition(StyleStructContext aContext)
   , mFlexGrow(0.0f)
   , mFlexShrink(1.0f)
   , mZIndex(eStyleUnit_Auto)
-  , mGridColumnGap(nscoord(0), nsStyleCoord::CoordConstructor)
-  , mGridRowGap(nscoord(0), nsStyleCoord::CoordConstructor)
+  , mColumnGap(eStyleUnit_Normal)
+  , mRowGap(eStyleUnit_Normal)
 {
   MOZ_COUNT_CTOR(nsStylePosition);
 
@@ -1489,8 +1486,8 @@ nsStylePosition::nsStylePosition(const nsStylePosition& aSource)
   , mGridColumnEnd(aSource.mGridColumnEnd)
   , mGridRowStart(aSource.mGridRowStart)
   , mGridRowEnd(aSource.mGridRowEnd)
-  , mGridColumnGap(aSource.mGridColumnGap)
-  , mGridRowGap(aSource.mGridRowGap)
+  , mColumnGap(aSource.mColumnGap)
+  , mRowGap(aSource.mRowGap)
 {
   MOZ_COUNT_CTOR(nsStylePosition);
 }
@@ -1590,8 +1587,8 @@ nsStylePosition::CalcDifference(const nsStylePosition& aNewData,
       mGridColumnEnd != aNewData.mGridColumnEnd ||
       mGridRowStart != aNewData.mGridRowStart ||
       mGridRowEnd != aNewData.mGridRowEnd ||
-      mGridColumnGap != aNewData.mGridColumnGap ||
-      mGridRowGap != aNewData.mGridRowGap) {
+      mColumnGap != aNewData.mColumnGap ||
+      mRowGap != aNewData.mRowGap) {
     return hint |
            nsChangeHint_AllReflowHints;
   }
diff --git a/layout/style/nsStyleStruct.h b/layout/style/nsStyleStruct.h
index 35ff071a55..a01685cc44 100644
--- a/layout/style/nsStyleStruct.h
+++ b/layout/style/nsStyleStruct.h
@@ -1848,8 +1848,8 @@ public:
   nsStyleGridLine mGridColumnEnd;
   nsStyleGridLine mGridRowStart;
   nsStyleGridLine mGridRowEnd;
-  nsStyleCoord    mGridColumnGap;       // [reset] coord, percent, calc
-  nsStyleCoord    mGridRowGap;          // [reset] coord, percent, calc
+  nsStyleCoord    mColumnGap;       // [reset] normal, coord, percent, calc
+  nsStyleCoord    mRowGap;          // [reset] normal, coord, percent, calc
 
   // FIXME: Logical-coordinate equivalents to these WidthDepends... and
   // HeightDepends... methods have been introduced (see below); we probably
@@ -3502,7 +3502,6 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleColumn
 
   uint32_t     mColumnCount; // [reset] see nsStyleConsts.h
   nsStyleCoord mColumnWidth; // [reset] coord, auto
-  nsStyleCoord mColumnGap;   // [reset] <length-percentage> | normal
 
   mozilla::StyleComplexColor mColumnRuleColor; // [reset]
   uint8_t      mColumnRuleStyle;  // [reset]
diff --git a/layout/style/test/property_database.js b/layout/style/test/property_database.js
index 1d5dc989f5..5c6e2f6d86 100644
--- a/layout/style/test/property_database.js
+++ b/layout/style/test/property_database.js
@@ -1432,23 +1432,6 @@ var gCSSProperties = {
     alias_for: "column-fill",
     subproperties: [ "column-fill" ]
   },
-  "column-gap": {
-    domProp: "columnGap",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: [ "normal", "1em", "calc(-2em + 3em)" ],
-    other_values: [ "2px", "1em", "4em", "3%", "calc(3%)", "calc(1em - 3%)",
-      "calc(2px)",
-      "calc(-2px)",
-      "calc(0px)",
-      "calc(0pt)",
-      "calc(5em)",
-      "calc(3*25px)",
-      "calc(25px*3)",
-      "calc(3*25px + 5em)",
-    ],
-    invalid_values: [ "-3%", "-1px", "4" ]
-  },
   "-moz-column-gap": {
     domProp: "MozColumnGap",
     inherited: false,
@@ -4147,6 +4130,8 @@ var gCSSProperties = {
       "calc(50px/(2 - 1))",
     ],
     invalid_values: [ "none", "-2px",
+      /* invalid for width but not flex-basis */
+      "content",
       /* invalid -moz-calc() values */
       "-moz-calc(50%+ 2px)",
       "-moz-calc(50% +2px)",
@@ -4662,12 +4647,18 @@ var gCSSProperties = {
     inherited: false,
     type: CSS_TYPE_LONGHAND,
     initial_values: [ " auto" ],
-        // NOTE: This is cribbed directly from the "width" chunk, since this
-        // property takes the exact same values as width (albeit with
-        // different semantics on 'auto').
-        // XXXdholbert (Maybe these should get separated out into
-        // a reusable array defined at the top of this file?)
-    other_values: [ "15px", "3em", "15%", "-moz-max-content", "-moz-min-content", "-moz-fit-content", "-moz-available",
+        // NOTE: Besides "content", this is cribbed directly from the "width"
+        // chunk, since this property takes the exact same values as width
+        // (plus 'content' & with different semantics on 'auto').
+    other_values: [
+      "15px",
+      "3em",
+      "15%",
+      "-moz-max-content",
+      "-moz-min-content",
+      "-moz-fit-content",
+      "-moz-available",
+      "content",
       // valid calc() values
       "calc(-2px)",
       "calc(2px)",
@@ -6187,561 +6178,581 @@ if (IsCSSPropertyPrefEnabled("layout.css.filters.enabled")) {
   };
 }
 
-if (IsCSSPropertyPrefEnabled("layout.css.grid.enabled")) {
-  var isGridTemplateSubgridValueEnabled =
-    IsCSSPropertyPrefEnabled("layout.css.grid-template-subgrid-value.enabled");
+var isGridTemplateSubgridValueEnabled =
+  IsCSSPropertyPrefEnabled("layout.css.grid-template-subgrid-value.enabled");
 
-  gCSSProperties["display"].other_values.push("grid", "inline-grid");
-  gCSSProperties["grid-auto-flow"] = {
-    domProp: "gridAutoFlow",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: [ "row" ],
-    other_values: [
-      "column",
-      "column dense",
-      "row dense",
-      "dense column",
-      "dense row",
-      "dense",
-    ],
-    invalid_values: [
-      "",
-      "auto",
-      "none",
-      "10px",
-      "column row",
-      "dense row dense",
-    ]
-  };
-
-  gCSSProperties["grid-auto-columns"] = {
-    domProp: "gridAutoColumns",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: [ "auto" ],
-    other_values: [
-      "40px",
-      "2em",
-      "2.5fr",
-      "12%",
-      "min-content",
-      "max-content",
-      "calc(2px - 99%)",
-      "minmax(20px, max-content)",
-      "minmax(min-content, auto)",
-      "minmax(auto, max-content)",
-      "m\\69nmax(20px, 4Fr)",
-      "MinMax(min-content, calc(20px + 10%))",
-      "fit-content(1px)",
-      "fit-content(calc(1px - 99%))",
-      "fit-content(10%)",
-    ],
-    invalid_values: [
-      "",
-      "normal",
-      "40ms",
-      "-40px",
-      "-12%",
-      "-2em",
-      "-2.5fr",
-      "minmax()",
-      "minmax(20px)",
-      "mİnmax(20px, 100px)",
-      "minmax(20px, 100px, 200px)",
-      "maxmin(100px, 20px)",
-      "minmax(min-content, minmax(30px, max-content))",
-      "fit-content(-1px)",
-      "fit-content(auto)",
-      "fit-content(min-content)",
-    ]
-  };
-  gCSSProperties["grid-auto-rows"] = {
-    domProp: "gridAutoRows",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: gCSSProperties["grid-auto-columns"].initial_values,
-    other_values: gCSSProperties["grid-auto-columns"].other_values,
-    invalid_values: gCSSProperties["grid-auto-columns"].invalid_values
-  };
-
-  gCSSProperties["grid-template-columns"] = {
-    domProp: "gridTemplateColumns",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: [ "none" ],
-    other_values: [
-      "auto",
-      "40px",
-      "2.5fr",
-      "[normal] 40px [] auto [ ] 12%",
-      "[foo] 40px min-content [ bar ] calc(2px - 99%) max-content",
-      "40px min-content calc(20px + 10%) max-content",
-      "minmax(min-content, auto)",
-      "minmax(auto, max-content)",
-      "m\\69nmax(20px, 4Fr)",
-      "40px MinMax(min-content, calc(20px + 10%)) max-content",
-      "40px 2em",
-      "[] 40px [-foo] 2em [bar baz This\ is\ one\ ident]",
-      // TODO bug 978478: "[a] repeat(3, [b] 20px [c] 40px [d]) [e]",
-      "repeat(1, 20px)",
-      "repeat(1, [a] 20px)",
-      "[a] Repeat(4, [a] 20px [] auto [b c]) [d]",
-      "[a] 2.5fr Repeat(4, [a] 20px [] auto [b c]) [d]",
-      "[a] 2.5fr [z] Repeat(4, [a] 20px [] auto [b c]) [d]",
-      "[a] 2.5fr [z] Repeat(4, [a] 20px [] auto) [d]",
-      "[a] 2.5fr [z] Repeat(4, 20px [b c] auto [b c]) [d]",
-      "[a] 2.5fr [z] Repeat(4, 20px auto) [d]",
-      "repeat(auto-fill, 0)",
-      "[a] repeat( Auto-fill,1%)",
-      "minmax(auto,0) [a] repeat(Auto-fit, 0) minmax(0,auto)",
-      "minmax(calc(1% + 1px),auto) repeat(Auto-fit,[] 1%) minmax(auto,1%)",
-      "[a] repeat( auto-fit,[a b] minmax(0,0) )",
-      "[a] 40px repeat(auto-fit,[a b] minmax(1px, 0) [])",
-      "[a] calc(1px - 99%) [b] repeat(auto-fit,[a b] minmax(1mm, 1%) [c]) [c]",
-      "repeat(auto-fill,minmax(1%,auto))",
-      "repeat(auto-fill,minmax(1em,min-content)) minmax(min-content,0)",
-      "repeat(auto-fill,minmax(max-content,1mm))",
-      "repeat(2, fit-content(1px))",
-      "fit-content(1px) 1fr",
-      "[a] fit-content(calc(1px - 99%)) [b]",
-      "[a] fit-content(10%) [b c] fit-content(1em)",
-    ],
-    invalid_values: [
-      "",
-      "normal",
-      "40ms",
-      "-40px",
-      "-12%",
-      "-2fr",
-      "[foo]",
-      "[inherit] 40px",
-      "[initial] 40px",
-      "[unset] 40px",
-      "[default] 40px",
-      "[span] 40px",
-      "[6%] 40px",
-      "[5th] 40px",
-      "[foo[] bar] 40px",
-      "[foo]] 40px",
-      "(foo) 40px",
-      "[foo] [bar] 40px",
-      "40px [foo] [bar]",
-      "minmax()",
-      "minmax(20px)",
-      "mİnmax(20px, 100px)",
-      "minmax(20px, 100px, 200px)",
-      "maxmin(100px, 20px)",
-      "minmax(min-content, minmax(30px, max-content))",
-      "repeat(0, 20px)",
-      "repeat(-3, 20px)",
-      "rêpeat(1, 20px)",
-      "repeat(1)",
-      "repeat(1, )",
-      "repeat(3px, 20px)",
-      "repeat(2.0, 20px)",
-      "repeat(2.5, 20px)",
-      "repeat(2, (foo))",
-      "repeat(2, foo)",
-      "40px calc(0px + rubbish)",
-      "repeat(1, repeat(1, 20px))",
-      "repeat(auto-fill, auto)",
-      "repeat(auto-fit,auto)",
-      "repeat(auto-fill, fit-content(1px))",
-      "repeat(auto-fit, fit-content(1px))",
-      "repeat(auto-fit,[])",
-      "repeat(auto-fill, 0) repeat(auto-fit, 0) ",
-      "repeat(auto-fit, 0) repeat(auto-fill, 0) ",
-      "[a] repeat(auto-fit, 0) repeat(auto-fit, 0) ",
-      "[a] repeat(auto-fill, 0) [a] repeat(auto-fill, 0) ",
-      "repeat(auto-fill, 0 0)",
-      "repeat(auto-fill, 0 [] 0)",
-      "repeat(auto-fill, min-content)",
-      "repeat(auto-fit,max-content)",
-      "repeat(auto-fit,1fr)",
-      "repeat(auto-fit,minmax(auto,auto))",
-      "repeat(auto-fit,minmax(min-content,1fr))",
-      "repeat(auto-fit,minmax(1fr,auto))",
-      "repeat(auto-fill,minmax(1fr,1em))",
-      "repeat(auto-fill, 10px) auto",
-      "auto repeat(auto-fit, 10px)",
-      "minmax(min-content,max-content) repeat(auto-fit, 0)",
-      "10px [a] 10px [b a] 1fr [b] repeat(auto-fill, 0)",
-      "fit-content(-1px)",
-      "fit-content(auto)",
-      "fit-content(min-content)",
-      "fit-content(1px) repeat(auto-fit, 1px)",
-      "fit-content(1px) repeat(auto-fill, 1px)",
-    ],
-    unbalanced_values: [
-      "(foo] 40px",
-    ]
-  };
-  if (isGridTemplateSubgridValueEnabled) {
-    gCSSProperties["grid-template-columns"].other_values.push(
-      // See https://bugzilla.mozilla.org/show_bug.cgi?id=981300
-      "[none auto subgrid min-content max-content foo] 40px",
-
-      "subgrid",
-      "subgrid [] [foo bar]",
-      "subgrid repeat(1, [])",
-      "subgrid Repeat(4, [a] [b c] [] [d])",
-      "subgrid repeat(auto-fill, [])",
-      "subgrid [x] repeat( Auto-fill, [a b c]) []",
-      "subgrid [x] repeat(auto-fill, []) [y z]"
-    );
-    gCSSProperties["grid-template-columns"].invalid_values.push(
-      "subgrid [inherit]",
-      "subgrid [initial]",
-      "subgrid [unset]",
-      "subgrid [default]",
-      "subgrid [span]",
-      "subgrid [foo] 40px",
-      "subgrid [foo 40px]",
-      "[foo] subgrid",
-      "subgrid rêpeat(1, [])",
-      "subgrid repeat(0, [])",
-      "subgrid repeat(-3, [])",
-      "subgrid repeat(2.0, [])",
-      "subgrid repeat(2.5, [])",
-      "subgrid repeat(3px, [])",
-      "subgrid repeat(1)",
-      "subgrid repeat(1, )",
-      "subgrid repeat(2, [40px])",
-      "subgrid repeat(2, foo)",
-      "subgrid repeat(1, repeat(1, []))",
-      "subgrid repeat(auto-fit,[])",
-      "subgrid [] repeat(auto-fit,[])",
-      "subgrid [a] repeat(auto-fit,[])",
-      "subgrid repeat(auto-fill, 1px)",
-      "subgrid repeat(auto-fill, 1px [])",
-      "subgrid repeat(Auto-fill, [a] [b c] [] [d])",
-      "subgrid repeat(auto-fill, []) repeat(auto-fill, [])"
-    );
-  }
-  gCSSProperties["grid-template-rows"] = {
-    domProp: "gridTemplateRows",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: gCSSProperties["grid-template-columns"].initial_values,
-    other_values: gCSSProperties["grid-template-columns"].other_values,
-    invalid_values: gCSSProperties["grid-template-columns"].invalid_values
-  };
-  gCSSProperties["grid-template-areas"] = {
-    domProp: "gridTemplateAreas",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: [ "none" ],
-    other_values: [
-      "''",
-      "'' ''",
-      "'1a-é_ .' \"b .\"",
-      "' Z\t\\aZ' 'Z Z'",
-      " '. . a b'  '. .a b' ",
-      "'a.b' '. . .'",
-      "'.' '..'",
-      "'...' '.'",
-      "'...-blah' '. .'",
-      "'.. ..' '.. ...'",
-    ],
-    invalid_values: [
-      "'a b' 'a/b'",
-      "'a . a'",
-      "'. a a' 'a a a'",
-      "'a a .' 'a a a'",
-      "'a a' 'a .'",
-      "'a a'\n'..'\n'a a'",
-    ]
-  };
-
-  gCSSProperties["grid-template"] = {
-    domProp: "gridTemplate",
-    inherited: false,
-    type: CSS_TYPE_TRUE_SHORTHAND,
-    subproperties: [
-      "grid-template-areas",
-      "grid-template-rows",
-      "grid-template-columns",
-    ],
-    initial_values: [
-      "none",
-      "none / none",
-    ],
-    other_values: [
-      // <'grid-template-rows'> / <'grid-template-columns'>
-      "40px / 100px",
-      "[foo] 40px [bar] / [baz] repeat(auto-fill,100px) [fizz]",
-      " none/100px",
-      "40px/none",
-      // [ <line-names>? <string> <track-size>? <line-names>? ]+ [ / <explicit-track-list> ]?
-      "'fizz'",
-      "[bar] 'fizz'",
-      "'fizz' / [foo] 40px",
-      "[bar] 'fizz' / [foo] 40px",
-      "'fizz' 100px / [foo] 40px",
-      "[bar] 'fizz' 100px / [foo] 40px",
-      "[bar] 'fizz' 100px [buzz] / [foo] 40px",
-      "[bar] 'fizz' 100px [buzz] \n [a] '.' 200px [b] / [foo] 40px",
-    ],
-    invalid_values: [
-      "'fizz' / repeat(1, 100px)",
-      "'fizz' repeat(1, 100px) / 0px",
-      "[foo] [bar] 40px / 100px",
-      "[fizz] [buzz] 100px / 40px",
-      "[fizz] [buzz] 'foo' / 40px",
-      "'foo' / none"
-    ]
-  };
-  if (isGridTemplateSubgridValueEnabled) {
-    gCSSProperties["grid-template"].other_values.push(
-      "subgrid",
-      "subgrid/40px 20px",
-      "subgrid [foo] [] [bar baz] / 40px 20px",
-      "40px 20px/subgrid",
-      "40px 20px/subgrid  [foo] [] repeat(3, [a] [b]) [bar baz]",
-      "subgrid/subgrid",
-      "subgrid [foo] [] [bar baz]/subgrid [foo] [] [bar baz]"
-    );
-    gCSSProperties["grid-template"].invalid_values.push(
-      "subgrid []",
-      "subgrid [] / 'fizz'",
-      "subgrid / 'fizz'"
-    );
-  }
-
-  gCSSProperties["grid"] = {
-    domProp: "grid",
-    inherited: false,
-    type: CSS_TYPE_TRUE_SHORTHAND,
-    subproperties: [
-      "grid-template-areas",
-      "grid-template-rows",
-      "grid-template-columns",
-      "grid-auto-flow",
-      "grid-auto-rows",
-      "grid-auto-columns",
-      "grid-column-gap",
-      "grid-row-gap",
-    ],
-    initial_values: [
-      "none",
-      "none / none",
-    ],
-    other_values: [
-      "auto-flow 40px / none",
-      "auto-flow / 40px",
-      "auto-flow dense auto / auto",
-      "dense auto-flow minmax(min-content, 2fr) / auto",
-      "dense auto-flow / 100px",
-      "none / auto-flow 40px",
-      "40px / auto-flow",
-      "none / dense auto-flow auto",
-    ].concat(
-      gCSSProperties["grid-template"].other_values
-    ),
-    invalid_values: [
-      "auto-flow",
-      " / auto-flow",
-      "dense 0 / 0",
-      "dense dense 40px / 0",
-      "auto-flow / auto-flow",
-      "auto-flow / dense",
-      "auto-flow [a] 0 / 0",
-      "0 / auto-flow [a] 0",
-      "auto-flow -20px / 0",
-      "auto-flow 200ms / 0",
-      "auto-flow 40px 100px / 0",
-    ].concat(
-      gCSSProperties["grid-template"].invalid_values,
-      gCSSProperties["grid-auto-flow"].other_values,
-      gCSSProperties["grid-auto-flow"].invalid_values
-        .filter((v) => v != 'none')
-    )
-  };
-
-  var gridLineOtherValues = [
-    "foo",
-    "2",
-    "2 foo",
-    "foo 2",
-    "-3",
-    "-3 bar",
-    "bar -3",
-    "span 2",
-    "2 span",
-    "span foo",
-    "foo span",
-    "span 2 foo",
-    "span foo 2",
-    "2 foo span",
-    "foo 2 span",
-  ];
-  var gridLineInvalidValues = [
+gCSSProperties["display"].other_values.push("grid", "inline-grid");
+gCSSProperties["grid-auto-flow"] = {
+  domProp: "gridAutoFlow",
+  inherited: false,
+  type: CSS_TYPE_LONGHAND,
+  initial_values: [ "row" ],
+  other_values: [
+    "column",
+    "column dense",
+    "row dense",
+    "dense column",
+    "dense row",
+    "dense",
+  ],
+  invalid_values: [
     "",
-    "4th",
-    "span",
-    "inherit 2",
-    "2 inherit",
-    "20px",
-    "2 3",
-    "2.5",
-    "2.0",
-    "0",
-    "0 foo",
-    "span 0",
-    "2 foo 3",
-    "foo 2 foo",
-    "2 span foo",
-    "foo span 2",
-    "span -3",
-    "span -3 bar",
-    "span 2 span",
-    "span foo span",
-    "span 2 foo span",
-  ];
+    "auto",
+    "none",
+    "10px",
+    "column row",
+    "dense row dense",
+  ]
+};
 
-  gCSSProperties["grid-column-start"] = {
-    domProp: "gridColumnStart",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: [ "auto" ],
-    other_values: gridLineOtherValues,
-    invalid_values: gridLineInvalidValues
-  };
-  gCSSProperties["grid-column-end"] = {
-    domProp: "gridColumnEnd",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: [ "auto" ],
-    other_values: gridLineOtherValues,
-    invalid_values: gridLineInvalidValues
-  };
-  gCSSProperties["grid-row-start"] = {
-    domProp: "gridRowStart",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: [ "auto" ],
-    other_values: gridLineOtherValues,
-    invalid_values: gridLineInvalidValues
-  };
-  gCSSProperties["grid-row-end"] = {
-    domProp: "gridRowEnd",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: [ "auto" ],
-    other_values: gridLineOtherValues,
-    invalid_values: gridLineInvalidValues
-  };
+gCSSProperties["grid-auto-columns"] = {
+  domProp: "gridAutoColumns",
+  inherited: false,
+  type: CSS_TYPE_LONGHAND,
+  initial_values: [ "auto" ],
+  other_values: [
+    "40px",
+    "2em",
+    "2.5fr",
+    "12%",
+    "min-content",
+    "max-content",
+    "calc(2px - 99%)",
+    "minmax(20px, max-content)",
+    "minmax(min-content, auto)",
+    "minmax(auto, max-content)",
+    "m\\69nmax(20px, 4Fr)",
+    "MinMax(min-content, calc(20px + 10%))",
+    "fit-content(1px)",
+    "fit-content(calc(1px - 99%))",
+    "fit-content(10%)",
+  ],
+  invalid_values: [
+    "",
+    "normal",
+    "40ms",
+    "-40px",
+    "-12%",
+    "-2em",
+    "-2.5fr",
+    "minmax()",
+    "minmax(20px)",
+    "mİnmax(20px, 100px)",
+    "minmax(20px, 100px, 200px)",
+    "maxmin(100px, 20px)",
+    "minmax(min-content, minmax(30px, max-content))",
+    "fit-content(-1px)",
+    "fit-content(auto)",
+    "fit-content(min-content)",
+  ]
+};
+gCSSProperties["grid-auto-rows"] = {
+  domProp: "gridAutoRows",
+  inherited: false,
+  type: CSS_TYPE_LONGHAND,
+  initial_values: gCSSProperties["grid-auto-columns"].initial_values,
+  other_values: gCSSProperties["grid-auto-columns"].other_values,
+  invalid_values: gCSSProperties["grid-auto-columns"].invalid_values
+};
 
-  // The grid-column and grid-row shorthands take values of the form
-  //   <grid-line> [ / <grid-line> ]?
-  var gridColumnRowOtherValues = [].concat(gridLineOtherValues);
-  gridLineOtherValues.concat([ "auto" ]).forEach(function(val) {
-    gridColumnRowOtherValues.push(" foo / " + val);
-    gridColumnRowOtherValues.push(val + "/2");
-  });
-  var gridColumnRowInvalidValues = [
-    "foo, bar",
-    "foo / bar / baz",
-  ].concat(gridLineInvalidValues);
-  gridLineInvalidValues.forEach(function(val) {
-    gridColumnRowInvalidValues.push("span 3 / " + val);
-    gridColumnRowInvalidValues.push(val + " / foo");
-  });
-  gCSSProperties["grid-column"] = {
-    domProp: "gridColumn",
-    inherited: false,
-    type: CSS_TYPE_TRUE_SHORTHAND,
-    subproperties: [
-      "grid-column-start",
-      "grid-column-end"
-    ],
-    initial_values: [ "auto", "auto / auto" ],
-    other_values: gridColumnRowOtherValues,
-    invalid_values: gridColumnRowInvalidValues
-  };
-  gCSSProperties["grid-row"] = {
-    domProp: "gridRow",
-    inherited: false,
-    type: CSS_TYPE_TRUE_SHORTHAND,
-    subproperties: [
-      "grid-row-start",
-      "grid-row-end"
-    ],
-    initial_values: [ "auto", "auto / auto" ],
-    other_values: gridColumnRowOtherValues,
-    invalid_values: gridColumnRowInvalidValues
-  };
+gCSSProperties["grid-template-columns"] = {
+  domProp: "gridTemplateColumns",
+  inherited: false,
+  type: CSS_TYPE_LONGHAND,
+  initial_values: [ "none" ],
+  other_values: [
+    "auto",
+    "40px",
+    "2.5fr",
+    "[normal] 40px [] auto [ ] 12%",
+    "[foo] 40px min-content [ bar ] calc(2px - 99%) max-content",
+    "40px min-content calc(20px + 10%) max-content",
+    "minmax(min-content, auto)",
+    "minmax(auto, max-content)",
+    "m\\69nmax(20px, 4Fr)",
+    "40px MinMax(min-content, calc(20px + 10%)) max-content",
+    "40px 2em",
+    "[] 40px [-foo] 2em [bar baz This\ is\ one\ ident]",
+    // TODO bug 978478: "[a] repeat(3, [b] 20px [c] 40px [d]) [e]",
+    "repeat(1, 20px)",
+    "repeat(1, [a] 20px)",
+    "[a] Repeat(4, [a] 20px [] auto [b c]) [d]",
+    "[a] 2.5fr Repeat(4, [a] 20px [] auto [b c]) [d]",
+    "[a] 2.5fr [z] Repeat(4, [a] 20px [] auto [b c]) [d]",
+    "[a] 2.5fr [z] Repeat(4, [a] 20px [] auto) [d]",
+    "[a] 2.5fr [z] Repeat(4, 20px [b c] auto [b c]) [d]",
+    "[a] 2.5fr [z] Repeat(4, 20px auto) [d]",
+    "repeat(auto-fill, 0)",
+    "[a] repeat( Auto-fill,1%)",
+    "minmax(auto,0) [a] repeat(Auto-fit, 0) minmax(0,auto)",
+    "minmax(calc(1% + 1px),auto) repeat(Auto-fit,[] 1%) minmax(auto,1%)",
+    "[a] repeat( auto-fit,[a b] minmax(0,0) )",
+    "[a] 40px repeat(auto-fit,[a b] minmax(1px, 0) [])",
+    "[a] calc(1px - 99%) [b] repeat(auto-fit,[a b] minmax(1mm, 1%) [c]) [c]",
+    "repeat(auto-fill,minmax(1%,auto))",
+    "repeat(auto-fill,minmax(1em,min-content)) minmax(min-content,0)",
+    "repeat(auto-fill,minmax(max-content,1mm))",
+    "repeat(2, fit-content(1px))",
+    "fit-content(1px) 1fr",
+    "[a] fit-content(calc(1px - 99%)) [b]",
+    "[a] fit-content(10%) [b c] fit-content(1em)",
+  ],
+  invalid_values: [
+    "",
+    "normal",
+    "40ms",
+    "-40px",
+    "-12%",
+    "-2fr",
+    "[foo]",
+    "[inherit] 40px",
+    "[initial] 40px",
+    "[unset] 40px",
+    "[default] 40px",
+    "[span] 40px",
+    "[6%] 40px",
+    "[5th] 40px",
+    "[foo[] bar] 40px",
+    "[foo]] 40px",
+    "(foo) 40px",
+    "[foo] [bar] 40px",
+    "40px [foo] [bar]",
+    "minmax()",
+    "minmax(20px)",
+    "mİnmax(20px, 100px)",
+    "minmax(20px, 100px, 200px)",
+    "maxmin(100px, 20px)",
+    "minmax(min-content, minmax(30px, max-content))",
+    "repeat(0, 20px)",
+    "repeat(-3, 20px)",
+    "rêpeat(1, 20px)",
+    "repeat(1)",
+    "repeat(1, )",
+    "repeat(3px, 20px)",
+    "repeat(2.0, 20px)",
+    "repeat(2.5, 20px)",
+    "repeat(2, (foo))",
+    "repeat(2, foo)",
+    "40px calc(0px + rubbish)",
+    "repeat(1, repeat(1, 20px))",
+    "repeat(auto-fill, auto)",
+    "repeat(auto-fit,auto)",
+    "repeat(auto-fill, fit-content(1px))",
+    "repeat(auto-fit, fit-content(1px))",
+    "repeat(auto-fit,[])",
+    "repeat(auto-fill, 0) repeat(auto-fit, 0) ",
+    "repeat(auto-fit, 0) repeat(auto-fill, 0) ",
+    "[a] repeat(auto-fit, 0) repeat(auto-fit, 0) ",
+    "[a] repeat(auto-fill, 0) [a] repeat(auto-fill, 0) ",
+    "repeat(auto-fill, 0 0)",
+    "repeat(auto-fill, 0 [] 0)",
+    "repeat(auto-fill, min-content)",
+    "repeat(auto-fit,max-content)",
+    "repeat(auto-fit,1fr)",
+    "repeat(auto-fit,minmax(auto,auto))",
+    "repeat(auto-fit,minmax(min-content,1fr))",
+    "repeat(auto-fit,minmax(1fr,auto))",
+    "repeat(auto-fill,minmax(1fr,1em))",
+    "repeat(auto-fill, 10px) auto",
+    "auto repeat(auto-fit, 10px)",
+    "minmax(min-content,max-content) repeat(auto-fit, 0)",
+    "10px [a] 10px [b a] 1fr [b] repeat(auto-fill, 0)",
+    "fit-content(-1px)",
+    "fit-content(auto)",
+    "fit-content(min-content)",
+    "fit-content(1px) repeat(auto-fit, 1px)",
+    "fit-content(1px) repeat(auto-fill, 1px)",
+  ],
+  unbalanced_values: [
+    "(foo] 40px",
+  ]
+};
+if (isGridTemplateSubgridValueEnabled) {
+  gCSSProperties["grid-template-columns"].other_values.push(
+    // See https://bugzilla.mozilla.org/show_bug.cgi?id=981300
+    "[none auto subgrid min-content max-content foo] 40px",
 
-  var gridAreaOtherValues = gridLineOtherValues.slice();
-  gridLineOtherValues.forEach(function(val) {
-    gridAreaOtherValues.push("foo / " + val);
-    gridAreaOtherValues.push(val + "/2/3");
-    gridAreaOtherValues.push("foo / bar / " + val + " / baz");
-  });
-  var gridAreaInvalidValues = [
-    "foo, bar",
-    "foo / bar / baz / fizz / buzz",
-    "default / foo / bar / baz",
-    "foo / initial / bar / baz",
-    "foo / bar / inherit / baz",
-    "foo / bar / baz / unset",
-  ].concat(gridLineInvalidValues);
-  gridLineInvalidValues.forEach(function(val) {
-    gridAreaInvalidValues.push("foo / " + val);
-    gridAreaInvalidValues.push("foo / bar / " + val);
-    gridAreaInvalidValues.push("foo / 4 / bar / " + val);
-  });
-
-  gCSSProperties["grid-area"] = {
-    domProp: "gridArea",
-    inherited: false,
-    type: CSS_TYPE_TRUE_SHORTHAND,
-    subproperties: [
-      "grid-row-start",
-      "grid-column-start",
-      "grid-row-end",
-      "grid-column-end"
-    ],
-    initial_values: [
-      "auto",
-      "auto / auto",
-      "auto / auto / auto",
-      "auto / auto / auto / auto"
-    ],
-    other_values: gridAreaOtherValues,
-    invalid_values: gridAreaInvalidValues
-  };
-
-  gCSSProperties["grid-column-gap"] = {
-    domProp: "gridColumnGap",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: [ "0" ],
-    other_values: [ "2px", "2%", "1em", "calc(1px + 1em)", "calc(1%)",
-                    "calc(1% + 1ch)" , "calc(1px - 99%)" ],
-    invalid_values: [ "-1px", "auto", "none", "1px 1px", "-1%", "fit-content(1px)" ],
-  };
-  gCSSProperties["grid-row-gap"] = {
-    domProp: "gridRowGap",
-    inherited: false,
-    type: CSS_TYPE_LONGHAND,
-    initial_values: [ "0" ],
-    other_values: [ "2px", "2%", "1em", "calc(1px + 1em)", "calc(1%)",
-                    "calc(1% + 1ch)" , "calc(1px - 99%)" ],
-    invalid_values: [ "-1px", "auto", "none", "1px 1px", "-1%", "min-content" ],
-  };
-  gCSSProperties["grid-gap"] = {
-    domProp: "gridGap",
-    inherited: false,
-    type: CSS_TYPE_TRUE_SHORTHAND,
-    subproperties: [ "grid-column-gap", "grid-row-gap" ],
-    initial_values: [ "0", "0 0" ],
-    other_values: [ "1ch 0", "1px 1%", "1em 1px", "calc(1px) calc(1%)" ],
-    invalid_values: [ "-1px", "1px -1px", "1px 1px 1px", "inherit 1px",
-                      "1px auto" ]
-  };
+    "subgrid",
+    "subgrid [] [foo bar]",
+    "subgrid repeat(1, [])",
+    "subgrid Repeat(4, [a] [b c] [] [d])",
+    "subgrid repeat(auto-fill, [])",
+    "subgrid [x] repeat( Auto-fill, [a b c]) []",
+    "subgrid [x] repeat(auto-fill, []) [y z]"
+  );
+  gCSSProperties["grid-template-columns"].invalid_values.push(
+    "subgrid [inherit]",
+    "subgrid [initial]",
+    "subgrid [unset]",
+    "subgrid [default]",
+    "subgrid [span]",
+    "subgrid [foo] 40px",
+    "subgrid [foo 40px]",
+    "[foo] subgrid",
+    "subgrid rêpeat(1, [])",
+    "subgrid repeat(0, [])",
+    "subgrid repeat(-3, [])",
+    "subgrid repeat(2.0, [])",
+    "subgrid repeat(2.5, [])",
+    "subgrid repeat(3px, [])",
+    "subgrid repeat(1)",
+    "subgrid repeat(1, )",
+    "subgrid repeat(2, [40px])",
+    "subgrid repeat(2, foo)",
+    "subgrid repeat(1, repeat(1, []))",
+    "subgrid repeat(auto-fit,[])",
+    "subgrid [] repeat(auto-fit,[])",
+    "subgrid [a] repeat(auto-fit,[])",
+    "subgrid repeat(auto-fill, 1px)",
+    "subgrid repeat(auto-fill, 1px [])",
+    "subgrid repeat(Auto-fill, [a] [b c] [] [d])",
+    "subgrid repeat(auto-fill, []) repeat(auto-fill, [])"
+  );
 }
+gCSSProperties["grid-template-rows"] = {
+  domProp: "gridTemplateRows",
+  inherited: false,
+  type: CSS_TYPE_LONGHAND,
+  initial_values: gCSSProperties["grid-template-columns"].initial_values,
+  other_values: gCSSProperties["grid-template-columns"].other_values,
+  invalid_values: gCSSProperties["grid-template-columns"].invalid_values
+};
+gCSSProperties["grid-template-areas"] = {
+  domProp: "gridTemplateAreas",
+  inherited: false,
+  type: CSS_TYPE_LONGHAND,
+  initial_values: [ "none" ],
+  other_values: [
+    "''",
+    "'' ''",
+    "'1a-é_ .' \"b .\"",
+    "' Z\t\\aZ' 'Z Z'",
+    " '. . a b'  '. .a b' ",
+    "'a.b' '. . .'",
+    "'.' '..'",
+    "'...' '.'",
+    "'...-blah' '. .'",
+    "'.. ..' '.. ...'",
+  ],
+  invalid_values: [
+    "'a b' 'a/b'",
+    "'a . a'",
+    "'. a a' 'a a a'",
+    "'a a .' 'a a a'",
+    "'a a' 'a .'",
+    "'a a'\n'..'\n'a a'",
+  ]
+};
+
+gCSSProperties["grid-template"] = {
+  domProp: "gridTemplate",
+  inherited: false,
+  type: CSS_TYPE_TRUE_SHORTHAND,
+  subproperties: [
+    "grid-template-areas",
+    "grid-template-rows",
+    "grid-template-columns",
+  ],
+  initial_values: [
+    "none",
+    "none / none",
+  ],
+  other_values: [
+    // <'grid-template-rows'> / <'grid-template-columns'>
+    "40px / 100px",
+    "[foo] 40px [bar] / [baz] repeat(auto-fill,100px) [fizz]",
+    " none/100px",
+    "40px/none",
+    // [ <line-names>? <string> <track-size>? <line-names>? ]+ [ / <explicit-track-list> ]?
+    "'fizz'",
+    "[bar] 'fizz'",
+    "'fizz' / [foo] 40px",
+    "[bar] 'fizz' / [foo] 40px",
+    "'fizz' 100px / [foo] 40px",
+    "[bar] 'fizz' 100px / [foo] 40px",
+    "[bar] 'fizz' 100px [buzz] / [foo] 40px",
+    "[bar] 'fizz' 100px [buzz] \n [a] '.' 200px [b] / [foo] 40px",
+  ],
+  invalid_values: [
+    "'fizz' / repeat(1, 100px)",
+    "'fizz' repeat(1, 100px) / 0px",
+    "[foo] [bar] 40px / 100px",
+    "[fizz] [buzz] 100px / 40px",
+    "[fizz] [buzz] 'foo' / 40px",
+    "'foo' / none"
+  ]
+};
+if (isGridTemplateSubgridValueEnabled) {
+  gCSSProperties["grid-template"].other_values.push(
+    "subgrid",
+    "subgrid/40px 20px",
+    "subgrid [foo] [] [bar baz] / 40px 20px",
+    "40px 20px/subgrid",
+    "40px 20px/subgrid  [foo] [] repeat(3, [a] [b]) [bar baz]",
+    "subgrid/subgrid",
+    "subgrid [foo] [] [bar baz]/subgrid [foo] [] [bar baz]"
+  );
+  gCSSProperties["grid-template"].invalid_values.push(
+    "subgrid []",
+    "subgrid [] / 'fizz'",
+    "subgrid / 'fizz'"
+  );
+}
+
+gCSSProperties["grid"] = {
+  domProp: "grid",
+  inherited: false,
+  type: CSS_TYPE_TRUE_SHORTHAND,
+  subproperties: [
+    "grid-template-areas",
+    "grid-template-rows",
+    "grid-template-columns",
+    "grid-auto-flow",
+    "grid-auto-rows",
+    "grid-auto-columns",
+    "grid-column-gap",
+    "grid-row-gap",
+  ],
+  initial_values: [
+    "none",
+    "none / none",
+  ],
+  other_values: [
+    "auto-flow 40px / none",
+    "auto-flow / 40px",
+    "auto-flow dense auto / auto",
+    "dense auto-flow minmax(min-content, 2fr) / auto",
+    "dense auto-flow / 100px",
+    "none / auto-flow 40px",
+    "40px / auto-flow",
+    "none / dense auto-flow auto",
+  ].concat(
+    gCSSProperties["grid-template"].other_values
+  ),
+  invalid_values: [
+    "auto-flow",
+    " / auto-flow",
+    "dense 0 / 0",
+    "dense dense 40px / 0",
+    "auto-flow / auto-flow",
+    "auto-flow / dense",
+    "auto-flow [a] 0 / 0",
+    "0 / auto-flow [a] 0",
+    "auto-flow -20px / 0",
+    "auto-flow 200ms / 0",
+    "auto-flow 40px 100px / 0",
+  ].concat(
+    gCSSProperties["grid-template"].invalid_values,
+    gCSSProperties["grid-auto-flow"].other_values,
+    gCSSProperties["grid-auto-flow"].invalid_values
+      .filter((v) => v != 'none')
+  )
+};
+
+var gridLineOtherValues = [
+  "foo",
+  "2",
+  "2 foo",
+  "foo 2",
+  "-3",
+  "-3 bar",
+  "bar -3",
+  "span 2",
+  "2 span",
+  "span foo",
+  "foo span",
+  "span 2 foo",
+  "span foo 2",
+  "2 foo span",
+  "foo 2 span",
+];
+var gridLineInvalidValues = [
+  "",
+  "4th",
+  "span",
+  "inherit 2",
+  "2 inherit",
+  "20px",
+  "2 3",
+  "2.5",
+  "2.0",
+  "0",
+  "0 foo",
+  "span 0",
+  "2 foo 3",
+  "foo 2 foo",
+  "2 span foo",
+  "foo span 2",
+  "span -3",
+  "span -3 bar",
+  "span 2 span",
+  "span foo span",
+  "span 2 foo span",
+];
+
+gCSSProperties["grid-column-start"] = {
+  domProp: "gridColumnStart",
+  inherited: false,
+  type: CSS_TYPE_LONGHAND,
+  initial_values: [ "auto" ],
+  other_values: gridLineOtherValues,
+  invalid_values: gridLineInvalidValues
+};
+gCSSProperties["grid-column-end"] = {
+  domProp: "gridColumnEnd",
+  inherited: false,
+  type: CSS_TYPE_LONGHAND,
+  initial_values: [ "auto" ],
+  other_values: gridLineOtherValues,
+  invalid_values: gridLineInvalidValues
+};
+gCSSProperties["grid-row-start"] = {
+  domProp: "gridRowStart",
+  inherited: false,
+  type: CSS_TYPE_LONGHAND,
+  initial_values: [ "auto" ],
+  other_values: gridLineOtherValues,
+  invalid_values: gridLineInvalidValues
+};
+gCSSProperties["grid-row-end"] = {
+  domProp: "gridRowEnd",
+  inherited: false,
+  type: CSS_TYPE_LONGHAND,
+  initial_values: [ "auto" ],
+  other_values: gridLineOtherValues,
+  invalid_values: gridLineInvalidValues
+};
+
+// The grid-column and grid-row shorthands take values of the form
+//   <grid-line> [ / <grid-line> ]?
+var gridColumnRowOtherValues = [].concat(gridLineOtherValues);
+gridLineOtherValues.concat([ "auto" ]).forEach(function(val) {
+  gridColumnRowOtherValues.push(" foo / " + val);
+  gridColumnRowOtherValues.push(val + "/2");
+});
+var gridColumnRowInvalidValues = [
+  "foo, bar",
+  "foo / bar / baz",
+].concat(gridLineInvalidValues);
+gridLineInvalidValues.forEach(function(val) {
+  gridColumnRowInvalidValues.push("span 3 / " + val);
+  gridColumnRowInvalidValues.push(val + " / foo");
+});
+gCSSProperties["grid-column"] = {
+  domProp: "gridColumn",
+  inherited: false,
+  type: CSS_TYPE_TRUE_SHORTHAND,
+  subproperties: [
+    "grid-column-start",
+    "grid-column-end"
+  ],
+  initial_values: [ "auto", "auto / auto" ],
+  other_values: gridColumnRowOtherValues,
+  invalid_values: gridColumnRowInvalidValues
+};
+gCSSProperties["grid-row"] = {
+  domProp: "gridRow",
+  inherited: false,
+  type: CSS_TYPE_TRUE_SHORTHAND,
+  subproperties: [
+    "grid-row-start",
+    "grid-row-end"
+  ],
+  initial_values: [ "auto", "auto / auto" ],
+  other_values: gridColumnRowOtherValues,
+  invalid_values: gridColumnRowInvalidValues
+};
+
+var gridAreaOtherValues = gridLineOtherValues.slice();
+gridLineOtherValues.forEach(function(val) {
+  gridAreaOtherValues.push("foo / " + val);
+  gridAreaOtherValues.push(val + "/2/3");
+  gridAreaOtherValues.push("foo / bar / " + val + " / baz");
+});
+var gridAreaInvalidValues = [
+  "foo, bar",
+  "foo / bar / baz / fizz / buzz",
+  "default / foo / bar / baz",
+  "foo / initial / bar / baz",
+  "foo / bar / inherit / baz",
+  "foo / bar / baz / unset",
+].concat(gridLineInvalidValues);
+gridLineInvalidValues.forEach(function(val) {
+  gridAreaInvalidValues.push("foo / " + val);
+  gridAreaInvalidValues.push("foo / bar / " + val);
+  gridAreaInvalidValues.push("foo / 4 / bar / " + val);
+});
+
+gCSSProperties["grid-area"] = {
+  domProp: "gridArea",
+  inherited: false,
+  type: CSS_TYPE_TRUE_SHORTHAND,
+  subproperties: [
+    "grid-row-start",
+    "grid-column-start",
+    "grid-row-end",
+    "grid-column-end"
+  ],
+  initial_values: [
+    "auto",
+    "auto / auto",
+    "auto / auto / auto",
+    "auto / auto / auto / auto"
+  ],
+  other_values: gridAreaOtherValues,
+  invalid_values: gridAreaInvalidValues
+};
+
+gCSSProperties["column-gap"] = {
+  domProp: "columnGap",
+  inherited: false,
+  type: CSS_TYPE_LONGHAND,
+  initial_values: [ "normal" ],
+  other_values: [ "2px", "2%", "1em", "calc(1px + 1em)", "calc(1%)",
+                  "calc(1% + 1ch)" , "calc(1px - 99%)" ],
+  invalid_values: [ "-1px", "auto", "none", "1px 1px", "-1%", "fit-content(1px)" ],
+};
+gCSSProperties["grid-column-gap"] = {
+  domProp: "gridColumnGap",
+  inherited: false,
+  type: CSS_TYPE_SHORTHAND_AND_LONGHAND,
+  alias_for: "column-gap",
+  subproperties: [ "column-gap" ]
+};
+gCSSProperties["row-gap"] = {
+  domProp: "rowGap",
+  inherited: false,
+  type: CSS_TYPE_LONGHAND,
+  initial_values: [ "normal" ],
+  other_values: [ "2px", "2%", "1em", "calc(1px + 1em)", "calc(1%)",
+                  "calc(1% + 1ch)" , "calc(1px - 99%)" ],
+  invalid_values: [ "-1px", "auto", "none", "1px 1px", "-1%", "min-content" ],
+};
+gCSSProperties["grid-row-gap"] = {
+  domProp: "gridRowGap",
+  inherited: false,
+  type: CSS_TYPE_SHORTHAND_AND_LONGHAND,
+  alias_for: "row-gap",
+  subproperties: [ "row-gap" ]
+};
+gCSSProperties["gap"] = {
+  domProp: "gap",
+  inherited: false,
+  type: CSS_TYPE_TRUE_SHORTHAND,
+  subproperties: [ "column-gap", "row-gap" ],
+  initial_values: [ "normal", "normal normal" ],
+  other_values: [ "1ch 0", "1px 1%", "1em 1px", "calc(1px) calc(1%)",
+                  "normal 0", "1% normal" ],
+  invalid_values: [ "-1px", "1px -1px", "1px 1px 1px", "inherit 1px",
+                    "1px auto" ]
+};
+gCSSProperties["grid-gap"] = {
+  domProp: "gridGap",
+  inherited: false,
+  type: CSS_TYPE_TRUE_SHORTHAND,
+  alias_for: "gap",
+  subproperties: [ "column-gap", "row-gap" ],
+};
 
 if (IsCSSPropertyPrefEnabled("layout.css.display-contents.enabled")) {
   gCSSProperties["display"].other_values.push("contents");
diff --git a/layout/style/test/test_transitions_per_property.html b/layout/style/test/test_transitions_per_property.html
index 83524b60d9..2e300fbe83 100644
--- a/layout/style/test/test_transitions_per_property.html
+++ b/layout/style/test/test_transitions_per_property.html
@@ -69,8 +69,6 @@ var supported_properties = {
     "box-shadow": [ test_shadow_transition ],
     "column-count": [ test_pos_integer_or_auto_transition,
                       test_integer_at_least_one_clamping ],
-    "column-gap": [ test_length_transition,
-                    test_length_clamped ],
     "column-rule-color": [ test_color_transition,
                            test_true_currentcolor_transition ],
     "column-rule-width": [ test_length_transition,
@@ -161,8 +159,8 @@ var supported_properties = {
                           /* test_float_zeroToOne_clamped */ ],
     "font-stretch": [ test_font_stretch ],
     "font-weight": [ test_font_weight ],
-    "grid-column-gap": [ test_grid_gap ],
-    "grid-row-gap": [ test_grid_gap ],
+    "column-gap": [ test_gap ],
+    "row-gap": [ test_gap ],
     "height": [ test_length_transition, test_percent_transition,
                 test_length_percent_calc_transition,
                 test_length_clamped, test_percent_clamped ],
@@ -1922,10 +1920,7 @@ function test_font_weight(prop) {
   div.style.setProperty("transition-timing-function", "linear", "");
 }
 
-function test_grid_gap(prop) {
-  if (!SpecialPowers.getBoolPref("layout.css.grid.enabled")) {
-    return;
-  }
+function test_gap(prop) {
   test_length_transition(prop);
   test_length_clamped(prop);
   test_percent_transition(prop);
diff --git a/modules/libmar/src/mar.h b/modules/libmar/src/mar.h
index 776daf648d..e9c8d555e4 100644
--- a/modules/libmar/src/mar.h
+++ b/modules/libmar/src/mar.h
@@ -109,7 +109,7 @@ int mar_enum_items(MarFile *mar, MarItemCallback callback, void *data);
  * @return          The number of bytes written or a negative value if an
  *                  error occurs.
  */
-int mar_read(MarFile *mar, const MarItem *item, int offset, char *buf,
+int mar_read(MarFile *mar, const MarItem *item, int offset, uint8_t *buf,
              int bufsize);
 
 /**
diff --git a/modules/libmar/src/mar_extract.c b/modules/libmar/src/mar_extract.c
index ec1cd6c534..969697ee29 100644
--- a/modules/libmar/src/mar_extract.c
+++ b/modules/libmar/src/mar_extract.c
@@ -37,7 +37,7 @@ static int mar_ensure_parent_dir(const char *path)
 
 static int mar_test_callback(MarFile *mar, const MarItem *item, void *unused) {
   FILE *fp;
-  char buf[BLOCKSIZE];
+  uint8_t buf[BLOCKSIZE];
   int fd, len, offset = 0;
 
   if (mar_ensure_parent_dir(item->name))
diff --git a/modules/libmar/src/mar_read.c b/modules/libmar/src/mar_read.c
index 241d0c08e4..89b9da27d6 100644
--- a/modules/libmar/src/mar_read.c
+++ b/modules/libmar/src/mar_read.c
@@ -530,7 +530,7 @@ int mar_enum_items(MarFile *mar, MarItemCallback callback, void *closure) {
   return 0;
 }
 
-int mar_read(MarFile *mar, const MarItem *item, int offset, char *buf,
+int mar_read(MarFile *mar, const MarItem *item, int offset, uint8_t *buf,
              int bufsize) {
   int nr;
 
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index 53947f3c96..e4be078407 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -2547,9 +2547,6 @@ pref("layout.css.variables.enabled", true);
 // Is support for CSS overflow-clip-box enabled for non-UA sheets?
 pref("layout.css.overflow-clip-box.enabled", false);
 
-// Is support for CSS grid enabled?
-pref("layout.css.grid.enabled", true);
-
 // Is support for CSS "grid-template-{columns,rows}: subgrid X" enabled?
 pref("layout.css.grid-template-subgrid-value.enabled", false);
 
diff --git a/modules/xz-embedded/README.mozilla b/modules/xz-embedded/README.mozilla
index d0532e1e91..17dd755ee4 100644
--- a/modules/xz-embedded/README.mozilla
+++ b/modules/xz-embedded/README.mozilla
@@ -1,14 +1,14 @@
 This is the XZ Embedded decompression library from
-http://tukaani.org/xz/embedded.html.
+https://tukaani.org/xz/embedded.html.
 
 Upstream code can be viewed at
-  http://git.tukaani.org/xz-embedded.git
+  https://git.tukaani.org/xz-embedded.git
 
 and cloned by
-  git clone http://git.tukaani.org/xz-embedded.git
+  git clone https://git.tukaani.org/xz-embedded.git
 
 The in-tree copy is updated by running
   sh update.sh
 from within the modules/xz-embedded directory.
 
-Current version: [e75f4eb79165213a02d567940d344f5c2ff1be03].
+Current version: [3f438e15109229bb14ab45f285f4bff5412a9542].
diff --git a/modules/xz-embedded/moz.build b/modules/xz-embedded/moz.build
index fa1e5fc468..9806dca1ea 100644
--- a/modules/xz-embedded/moz.build
+++ b/modules/xz-embedded/moz.build
@@ -29,4 +29,7 @@ elif '86' in CONFIG['TARGET_CPU']:
 
 DEFINES['XZ_USE_CRC64'] = 1
 
+if CONFIG['OS_ARCH'] == 'WINNT':
+    USE_STATIC_LIBS = True
+
 Library('xz-embedded')
diff --git a/modules/xz-embedded/src/xz.h b/modules/xz-embedded/src/xz.h
index 0a4b38d33c..f3801eb6f5 100644
--- a/modules/xz-embedded/src/xz.h
+++ b/modules/xz-embedded/src/xz.h
@@ -2,7 +2,7 @@
  * XZ decompressor
  *
  * Authors: Lasse Collin <lasse.collin@tukaani.org>
- *          Igor Pavlov <http://7-zip.org/>
+ *          Igor Pavlov <https://7-zip.org/>
  *
  * This file has been put into the public domain.
  * You can do whatever you want with this file.
@@ -32,7 +32,7 @@ extern "C" {
  * enum xz_mode - Operation mode
  *
  * @XZ_SINGLE:              Single-call mode. This uses less RAM than
- *                          than multi-call modes, because the LZMA2
+ *                          multi-call modes, because the LZMA2
  *                          dictionary doesn't need to be allocated as
  *                          part of the decoder state. All required data
  *                          structures are allocated at initialization,
@@ -198,7 +198,7 @@ struct xz_dec;
 XZ_EXTERN struct xz_dec *xz_dec_init(enum xz_mode mode, uint32_t dict_max);
 
 /**
- * xz_dec_run() - Run the XZ decoder
+ * xz_dec_run() - Run the XZ decoder for a single XZ stream
  * @s:          Decoder state allocated using xz_dec_init()
  * @b:          Input and output buffers
  *
@@ -214,9 +214,51 @@ XZ_EXTERN struct xz_dec *xz_dec_init(enum xz_mode mode, uint32_t dict_max);
  * cannot give the single-call decoder a too small buffer and then expect to
  * get that amount valid data from the beginning of the stream. You must use
  * the multi-call decoder if you don't want to uncompress the whole stream.
+ *
+ * Use xz_dec_run() when XZ data is stored inside some other file format.
+ * The decoding will stop after one XZ stream has been decompresed. To
+ * decompress regular .xz files which might have multiple concatenated
+ * streams, use xz_dec_catrun() instead.
  */
 XZ_EXTERN enum xz_ret xz_dec_run(struct xz_dec *s, struct xz_buf *b);
 
+/**
+ * xz_dec_catrun() - Run the XZ decoder with support for concatenated streams
+ * @s:          Decoder state allocated using xz_dec_init()
+ * @b:          Input and output buffers
+ * @finish:     This is an int instead of bool to avoid requiring stdbool.h.
+ *              As long as more input might be coming, finish must be false.
+ *              When the caller knows that it has provided all the input to
+ *              the decoder (some possibly still in b->in), it must set finish
+ *              to true. Only when finish is true can this function return
+ *              XZ_STREAM_END to indicate successful decompression of the
+ *              file. In single-call mode (XZ_SINGLE) finish is assumed to
+ *              always be true; the caller-provided value is ignored.
+ *
+ * This is like xz_dec_run() except that this makes it easy to decode .xz
+ * files with multiple streams (multiple .xz files concatenated as is).
+ * The rarely-used Stream Padding feature is supported too, that is, there
+ * can be null bytes after or between the streams. The number of null bytes
+ * must be a multiple of four.
+ *
+ * When finish is false and b->in_pos == b->in_size, it is possible that
+ * XZ_BUF_ERROR isn't returned even when no progress is possible (XZ_OK is
+ * returned instead). This shouldn't matter because in this situation a
+ * reasonable caller will attempt to provide more input or set finish to
+ * true for the next xz_dec_catrun() call anyway.
+ *
+ * For any struct xz_dec that has been initialized for multi-call mode:
+ * Once decoding has been started with xz_dec_run() or xz_dec_catrun(),
+ * the same function must be used until xz_dec_reset() or xz_dec_end().
+ * Switching between the two decoding functions without resetting results
+ * in undefined behavior.
+ *
+ * xz_dec_catrun() is only available if XZ_DEC_CONCATENATED was defined
+ * at compile time.
+ */
+XZ_EXTERN enum xz_ret xz_dec_catrun(struct xz_dec *s, struct xz_buf *b,
+				    int finish);
+
 /**
  * xz_dec_reset() - Reset an already allocated decoder state
  * @s:          Decoder state allocated using xz_dec_init()
@@ -237,6 +279,112 @@ XZ_EXTERN void xz_dec_reset(struct xz_dec *s);
  */
 XZ_EXTERN void xz_dec_end(struct xz_dec *s);
 
+/*
+ * Decompressor for MicroLZMA, an LZMA variant with a very minimal header.
+ * See xz_dec_microlzma_alloc() below for details.
+ *
+ * These functions aren't used or available in preboot code and thus aren't
+ * marked with XZ_EXTERN. This avoids warnings about static functions that
+ * are never defined.
+ */
+/**
+ * struct xz_dec_microlzma - Opaque type to hold the MicroLZMA decoder state
+ */
+struct xz_dec_microlzma;
+
+/**
+ * xz_dec_microlzma_alloc() - Allocate memory for the MicroLZMA decoder
+ * @mode        XZ_SINGLE or XZ_PREALLOC
+ * @dict_size   LZMA dictionary size. This must be at least 4 KiB and
+ *              at most 3 GiB.
+ *
+ * In contrast to xz_dec_init(), this function only allocates the memory
+ * and remembers the dictionary size. xz_dec_microlzma_reset() must be used
+ * before calling xz_dec_microlzma_run().
+ *
+ * The amount of allocated memory is a little less than 30 KiB with XZ_SINGLE.
+ * With XZ_PREALLOC also a dictionary buffer of dict_size bytes is allocated.
+ *
+ * On success, xz_dec_microlzma_alloc() returns a pointer to
+ * struct xz_dec_microlzma. If memory allocation fails or
+ * dict_size is invalid, NULL is returned.
+ *
+ * The compressed format supported by this decoder is a raw LZMA stream
+ * whose first byte (always 0x00) has been replaced with bitwise-negation
+ * of the LZMA properties (lc/lp/pb) byte. For example, if lc/lp/pb is
+ * 3/0/2, the first byte is 0xA2. This way the first byte can never be 0x00.
+ * Just like with LZMA2, lc + lp <= 4 must be true. The LZMA end-of-stream
+ * marker must not be used. The unused values are reserved for future use.
+ * This MicroLZMA header format was created for use in EROFS but may be used
+ * by others too.
+ */
+extern struct xz_dec_microlzma *xz_dec_microlzma_alloc(enum xz_mode mode,
+						       uint32_t dict_size);
+
+/**
+ * xz_dec_microlzma_reset() - Reset the MicroLZMA decoder state
+ * @s           Decoder state allocated using xz_dec_microlzma_alloc()
+ * @comp_size   Compressed size of the input stream
+ * @uncomp_size Uncompressed size of the input stream. A value smaller
+ *              than the real uncompressed size of the input stream can
+ *              be specified if uncomp_size_is_exact is set to false.
+ *              uncomp_size can never be set to a value larger than the
+ *              expected real uncompressed size because it would eventually
+ *              result in XZ_DATA_ERROR.
+ * @uncomp_size_is_exact  This is an int instead of bool to avoid
+ *              requiring stdbool.h. This should normally be set to true.
+ *              When this is set to false, error detection is weaker.
+ */
+extern void xz_dec_microlzma_reset(struct xz_dec_microlzma *s,
+				   uint32_t comp_size, uint32_t uncomp_size,
+				   int uncomp_size_is_exact);
+
+/**
+ * xz_dec_microlzma_run() - Run the MicroLZMA decoder
+ * @s           Decoder state initialized using xz_dec_microlzma_reset()
+ * @b:          Input and output buffers
+ *
+ * This works similarly to xz_dec_run() with a few important differences.
+ * Only the differences are documented here.
+ *
+ * The only possible return values are XZ_OK, XZ_STREAM_END, and
+ * XZ_DATA_ERROR. This function cannot return XZ_BUF_ERROR: if no progress
+ * is possible due to lack of input data or output space, this function will
+ * keep returning XZ_OK. Thus, the calling code must be written so that it
+ * will eventually provide input and output space matching (or exceeding)
+ * comp_size and uncomp_size arguments given to xz_dec_microlzma_reset().
+ * If the caller cannot do this (for example, if the input file is truncated
+ * or otherwise corrupt), the caller must detect this error by itself to
+ * avoid an infinite loop.
+ *
+ * If the compressed data seems to be corrupt, XZ_DATA_ERROR is returned.
+ * This can happen also when incorrect dictionary, uncompressed, or
+ * compressed sizes have been specified.
+ *
+ * With XZ_PREALLOC only: As an extra feature, b->out may be NULL to skip over
+ * uncompressed data. This way the caller doesn't need to provide a temporary
+ * output buffer for the bytes that will be ignored.
+ *
+ * With XZ_SINGLE only: In contrast to xz_dec_run(), the return value XZ_OK
+ * is also possible and thus XZ_SINGLE is actually a limited multi-call mode.
+ * After XZ_OK the bytes decoded so far may be read from the output buffer.
+ * It is possible to continue decoding but the variables b->out and b->out_pos
+ * MUST NOT be changed by the caller. Increasing the value of b->out_size is
+ * allowed to make more output space available; one doesn't need to provide
+ * space for the whole uncompressed data on the first call. The input buffer
+ * may be changed normally like with XZ_PREALLOC. This way input data can be
+ * provided from non-contiguous memory.
+ */
+extern enum xz_ret xz_dec_microlzma_run(struct xz_dec_microlzma *s,
+					struct xz_buf *b);
+
+/**
+ * xz_dec_microlzma_end() - Free the memory allocated for the decoder state
+ * @s:          Decoder state allocated using xz_dec_microlzma_alloc().
+ *              If s is NULL, this function does nothing.
+ */
+extern void xz_dec_microlzma_end(struct xz_dec_microlzma *s);
+
 /*
  * Standalone build (userspace build or in-kernel build for boot time use)
  * needs a CRC32 implementation. For normal in-kernel use, kernel's own
diff --git a/modules/xz-embedded/src/xz_config.h b/modules/xz-embedded/src/xz_config.h
index eb9dac1a4b..ee590d7ea6 100644
--- a/modules/xz-embedded/src/xz_config.h
+++ b/modules/xz-embedded/src/xz_config.h
@@ -10,6 +10,9 @@
 #ifndef XZ_CONFIG_H
 #define XZ_CONFIG_H
 
+/* Uncomment to enable building of xz_dec_catrun(). */
+/* #define XZ_DEC_CONCATENATED */
+
 /* Uncomment to enable CRC64 support. */
 /* #define XZ_USE_CRC64 */
 
diff --git a/modules/xz-embedded/src/xz_crc32.c b/modules/xz-embedded/src/xz_crc32.c
index 34532d14fd..5627b00fca 100644
--- a/modules/xz-embedded/src/xz_crc32.c
+++ b/modules/xz-embedded/src/xz_crc32.c
@@ -2,7 +2,7 @@
  * CRC32 using the polynomial from IEEE-802.3
  *
  * Authors: Lasse Collin <lasse.collin@tukaani.org>
- *          Igor Pavlov <http://7-zip.org/>
+ *          Igor Pavlov <https://7-zip.org/>
  *
  * This file has been put into the public domain.
  * You can do whatever you want with this file.
diff --git a/modules/xz-embedded/src/xz_crc64.c b/modules/xz-embedded/src/xz_crc64.c
index ca1caee899..60c40f67e7 100644
--- a/modules/xz-embedded/src/xz_crc64.c
+++ b/modules/xz-embedded/src/xz_crc64.c
@@ -4,7 +4,7 @@
  * This file is similar to xz_crc32.c. See the comments there.
  *
  * Authors: Lasse Collin <lasse.collin@tukaani.org>
- *          Igor Pavlov <http://7-zip.org/>
+ *          Igor Pavlov <https://7-zip.org/>
  *
  * This file has been put into the public domain.
  * You can do whatever you want with this file.
@@ -20,7 +20,11 @@ STATIC_RW_DATA uint64_t xz_crc64_table[256];
 
 XZ_EXTERN void xz_crc64_init(void)
 {
-	const uint64_t poly = 0xC96C5795D7870F42;
+	/*
+	 * The ULL suffix is needed for -std=gnu89 compatibility
+	 * on 32-bit platforms.
+	 */
+	const uint64_t poly = 0xC96C5795D7870F42ULL;
 
 	uint32_t i;
 	uint32_t j;
diff --git a/modules/xz-embedded/src/xz_dec_bcj.c b/modules/xz-embedded/src/xz_dec_bcj.c
index a768e6d28b..ef449e97d1 100644
--- a/modules/xz-embedded/src/xz_dec_bcj.c
+++ b/modules/xz-embedded/src/xz_dec_bcj.c
@@ -2,7 +2,7 @@
  * Branch/Call/Jump (BCJ) filter decoders
  *
  * Authors: Lasse Collin <lasse.collin@tukaani.org>
- *          Igor Pavlov <http://7-zip.org/>
+ *          Igor Pavlov <https://7-zip.org/>
  *
  * This file has been put into the public domain.
  * You can do whatever you want with this file.
@@ -422,7 +422,7 @@ XZ_EXTERN enum xz_ret xz_dec_bcj_run(struct xz_dec_bcj *s,
 
 	/*
 	 * Flush pending already filtered data to the output buffer. Return
-	 * immediatelly if we couldn't flush everything, or if the next
+	 * immediately if we couldn't flush everything, or if the next
 	 * filter in the chain had already returned XZ_STREAM_END.
 	 */
 	if (s->temp.filtered > 0) {
diff --git a/modules/xz-embedded/src/xz_dec_lzma2.c b/modules/xz-embedded/src/xz_dec_lzma2.c
index 08c3c80499..c929f1c82b 100644
--- a/modules/xz-embedded/src/xz_dec_lzma2.c
+++ b/modules/xz-embedded/src/xz_dec_lzma2.c
@@ -2,7 +2,7 @@
  * LZMA2 decoder
  *
  * Authors: Lasse Collin <lasse.collin@tukaani.org>
- *          Igor Pavlov <http://7-zip.org/>
+ *          Igor Pavlov <https://7-zip.org/>
  *
  * This file has been put into the public domain.
  * You can do whatever you want with this file.
@@ -147,8 +147,8 @@ struct lzma_dec {
 
 	/*
 	 * LZMA properties or related bit masks (number of literal
-	 * context bits, a mask dervied from the number of literal
-	 * position bits, and a mask dervied from the number
+	 * context bits, a mask derived from the number of literal
+	 * position bits, and a mask derived from the number
 	 * position bits)
 	 */
 	uint32_t lc;
@@ -248,6 +248,10 @@ struct lzma2_dec {
 	 * before the first LZMA chunk.
 	 */
 	bool need_props;
+
+#ifdef XZ_DEC_MICROLZMA
+	bool pedantic_microlzma;
+#endif
 };
 
 struct xz_dec_lzma2 {
@@ -387,7 +391,14 @@ static void dict_uncompressed(struct dictionary *dict, struct xz_buf *b,
 
 		*left -= copy_size;
 
-		memcpy(dict->buf + dict->pos, b->in + b->in_pos, copy_size);
+		/*
+		 * If doing in-place decompression in single-call mode and the
+		 * uncompressed size of the file is larger than the caller
+		 * thought (i.e. it is invalid input!), the buffers below may
+		 * overlap and cause undefined behavior with memcpy().
+		 * With valid inputs memcpy() would be fine here.
+		 */
+		memmove(dict->buf + dict->pos, b->in + b->in_pos, copy_size);
 		dict->pos += copy_size;
 
 		if (dict->full < dict->pos)
@@ -397,7 +408,11 @@ static void dict_uncompressed(struct dictionary *dict, struct xz_buf *b,
 			if (dict->pos == dict->end)
 				dict->pos = 0;
 
-			memcpy(b->out + b->out_pos, b->in + b->in_pos,
+			/*
+			 * Like above but for multi-call mode: use memmove()
+			 * to avoid undefined behavior with invalid input.
+			 */
+			memmove(b->out + b->out_pos, b->in + b->in_pos,
 					copy_size);
 		}
 
@@ -408,6 +423,12 @@ static void dict_uncompressed(struct dictionary *dict, struct xz_buf *b,
 	}
 }
 
+#ifdef XZ_DEC_MICROLZMA
+#	define DICT_FLUSH_SUPPORTS_SKIPPING true
+#else
+#	define DICT_FLUSH_SUPPORTS_SKIPPING false
+#endif
+
 /*
  * Flush pending data from dictionary to b->out. It is assumed that there is
  * enough space in b->out. This is guaranteed because caller uses dict_limit()
@@ -421,8 +442,19 @@ static uint32_t dict_flush(struct dictionary *dict, struct xz_buf *b)
 		if (dict->pos == dict->end)
 			dict->pos = 0;
 
-		memcpy(b->out + b->out_pos, dict->buf + dict->start,
-				copy_size);
+		/*
+		 * These buffers cannot overlap even if doing in-place
+		 * decompression because in multi-call mode dict->buf
+		 * has been allocated by us in this file; it's not
+		 * provided by the caller like in single-call mode.
+		 *
+		 * With MicroLZMA, b->out can be NULL to skip bytes that
+		 * the caller doesn't need. This cannot be done with XZ
+		 * because it would break BCJ filters.
+		 */
+		if (!DICT_FLUSH_SUPPORTS_SKIPPING || b->out != NULL)
+			memcpy(b->out + b->out_pos, dict->buf + dict->start,
+					copy_size);
 	}
 
 	dict->start = dict->pos;
@@ -484,11 +516,11 @@ static __always_inline void rc_normalize(struct rc_dec *rc)
 }
 
 /*
- * Decode one bit. In some versions, this function has been splitted in three
+ * Decode one bit. In some versions, this function has been split in three
  * functions so that the compiler is supposed to be able to more easily avoid
  * an extra branch. In this particular version of the LZMA decoder, this
  * doesn't seem to be a good idea (tested with GCC 3.3.6, 3.4.6, and 4.3.3
- * on x86). Using a non-splitted version results in nicer looking code too.
+ * on x86). Using a non-split version results in nicer looking code too.
  *
  * NOTE: This must return an int. Do not make it return a bool or the speed
  * of the code generated by GCC 3.x decreases 10-15 %. (GCC 4.3 doesn't care,
@@ -761,7 +793,7 @@ static bool lzma_main(struct xz_dec_lzma2 *s)
 }
 
 /*
- * Reset the LZMA decoder and range decoder state. Dictionary is nore reset
+ * Reset the LZMA decoder and range decoder state. Dictionary is not reset
  * here, because LZMA state may be reset without resetting the dictionary.
  */
 static void lzma_reset(struct xz_dec_lzma2 *s)
@@ -774,6 +806,7 @@ static void lzma_reset(struct xz_dec_lzma2 *s)
 	s->lzma.rep1 = 0;
 	s->lzma.rep2 = 0;
 	s->lzma.rep3 = 0;
+	s->lzma.len = 0;
 
 	/*
 	 * All probabilities are initialized to the same value. This hack
@@ -1146,6 +1179,7 @@ XZ_EXTERN enum xz_ret xz_dec_lzma2_reset(struct xz_dec_lzma2 *s, uint8_t props)
 
 		if (DEC_IS_DYNALLOC(s->dict.mode)) {
 			if (s->dict.allocated < s->dict.size) {
+				s->dict.allocated = s->dict.size;
 				vfree(s->dict.buf);
 				s->dict.buf = vmalloc(s->dict.size);
 				if (s->dict.buf == NULL) {
@@ -1156,8 +1190,6 @@ XZ_EXTERN enum xz_ret xz_dec_lzma2_reset(struct xz_dec_lzma2 *s, uint8_t props)
 		}
 	}
 
-	s->lzma.len = 0;
-
 	s->lzma2.sequence = SEQ_CONTROL;
 	s->lzma2.need_dict_reset = true;
 
@@ -1173,3 +1205,140 @@ XZ_EXTERN void xz_dec_lzma2_end(struct xz_dec_lzma2 *s)
 
 	kfree(s);
 }
+
+#ifdef XZ_DEC_MICROLZMA
+/* This is a wrapper struct to have a nice struct name in the public API. */
+struct xz_dec_microlzma {
+	struct xz_dec_lzma2 s;
+};
+
+enum xz_ret xz_dec_microlzma_run(struct xz_dec_microlzma *s_ptr,
+				 struct xz_buf *b)
+{
+	struct xz_dec_lzma2 *s = &s_ptr->s;
+
+	/*
+	 * sequence is SEQ_PROPERTIES before the first input byte,
+	 * SEQ_LZMA_PREPARE until a total of five bytes have been read,
+	 * and SEQ_LZMA_RUN for the rest of the input stream.
+	 */
+	if (s->lzma2.sequence != SEQ_LZMA_RUN) {
+		if (s->lzma2.sequence == SEQ_PROPERTIES) {
+			/* One byte is needed for the props. */
+			if (b->in_pos >= b->in_size)
+				return XZ_OK;
+
+			/*
+			 * Don't increment b->in_pos here. The same byte is
+			 * also passed to rc_read_init() which will ignore it.
+			 */
+			if (!lzma_props(s, ~b->in[b->in_pos]))
+				return XZ_DATA_ERROR;
+
+			s->lzma2.sequence = SEQ_LZMA_PREPARE;
+		}
+
+		/*
+		 * xz_dec_microlzma_reset() doesn't validate the compressed
+		 * size so we do it here. We have to limit the maximum size
+		 * to avoid integer overflows in lzma2_lzma(). 3 GiB is a nice
+		 * round number and much more than users of this code should
+		 * ever need.
+		 */
+		if (s->lzma2.compressed < RC_INIT_BYTES
+				|| s->lzma2.compressed > (3U << 30))
+			return XZ_DATA_ERROR;
+
+		if (!rc_read_init(&s->rc, b))
+			return XZ_OK;
+
+		s->lzma2.compressed -= RC_INIT_BYTES;
+		s->lzma2.sequence = SEQ_LZMA_RUN;
+
+		dict_reset(&s->dict, b);
+	}
+
+	/* This is to allow increasing b->out_size between calls. */
+	if (DEC_IS_SINGLE(s->dict.mode))
+		s->dict.end = b->out_size - b->out_pos;
+
+	while (true) {
+		dict_limit(&s->dict, min_t(size_t, b->out_size - b->out_pos,
+					   s->lzma2.uncompressed));
+
+		if (!lzma2_lzma(s, b))
+			return XZ_DATA_ERROR;
+
+		s->lzma2.uncompressed -= dict_flush(&s->dict, b);
+
+		if (s->lzma2.uncompressed == 0) {
+			if (s->lzma2.pedantic_microlzma) {
+				if (s->lzma2.compressed > 0 || s->lzma.len > 0
+						|| !rc_is_finished(&s->rc))
+					return XZ_DATA_ERROR;
+			}
+
+			return XZ_STREAM_END;
+		}
+
+		if (b->out_pos == b->out_size)
+			return XZ_OK;
+
+		if (b->in_pos == b->in_size
+				&& s->temp.size < s->lzma2.compressed)
+			return XZ_OK;
+	}
+}
+
+struct xz_dec_microlzma *xz_dec_microlzma_alloc(enum xz_mode mode,
+						uint32_t dict_size)
+{
+	struct xz_dec_microlzma *s;
+
+	/* Restrict dict_size to the same range as in the LZMA2 code. */
+	if (dict_size < 4096 || dict_size > (3U << 30))
+		return NULL;
+
+	s = kmalloc(sizeof(*s), GFP_KERNEL);
+	if (s == NULL)
+		return NULL;
+
+	s->s.dict.mode = mode;
+	s->s.dict.size = dict_size;
+
+	if (DEC_IS_MULTI(mode)) {
+		s->s.dict.end = dict_size;
+
+		s->s.dict.buf = vmalloc(dict_size);
+		if (s->s.dict.buf == NULL) {
+			kfree(s);
+			return NULL;
+		}
+	}
+
+	return s;
+}
+
+void xz_dec_microlzma_reset(struct xz_dec_microlzma *s, uint32_t comp_size,
+			    uint32_t uncomp_size, int uncomp_size_is_exact)
+{
+	/*
+	 * comp_size is validated in xz_dec_microlzma_run().
+	 * uncomp_size can safely be anything.
+	 */
+	s->s.lzma2.compressed = comp_size;
+	s->s.lzma2.uncompressed = uncomp_size;
+	s->s.lzma2.pedantic_microlzma = uncomp_size_is_exact;
+
+	s->s.lzma2.sequence = SEQ_PROPERTIES;
+	s->s.temp.size = 0;
+}
+
+void xz_dec_microlzma_end(struct xz_dec_microlzma *s)
+{
+	if (DEC_IS_MULTI(s->s.dict.mode))
+		vfree(s->s.dict.buf);
+
+	kfree(s);
+}
+#endif
diff --git a/modules/xz-embedded/src/xz_dec_stream.c b/modules/xz-embedded/src/xz_dec_stream.c
index d6525506a1..2c41f5f1b0 100644
--- a/modules/xz-embedded/src/xz_dec_stream.c
+++ b/modules/xz-embedded/src/xz_dec_stream.c
@@ -35,7 +35,8 @@ struct xz_dec {
 		SEQ_INDEX,
 		SEQ_INDEX_PADDING,
 		SEQ_INDEX_CRC32,
-		SEQ_STREAM_FOOTER
+		SEQ_STREAM_FOOTER,
+		SEQ_STREAM_PADDING
 	} sequence;
 
 	/* Position in variable-length integers and Check fields */
@@ -423,12 +424,12 @@ static enum xz_ret dec_stream_header(struct xz_dec *s)
 	 * check types too, but then the check won't be verified and
 	 * a warning (XZ_UNSUPPORTED_CHECK) will be given.
 	 */
+	if (s->temp.buf[HEADER_MAGIC_SIZE + 1] > XZ_CHECK_MAX)
+		return XZ_OPTIONS_ERROR;
+
 	s->check_type = s->temp.buf[HEADER_MAGIC_SIZE + 1];
 
 #ifdef XZ_DEC_ANY_CHECK
-	if (s->check_type > XZ_CHECK_MAX)
-		return XZ_OPTIONS_ERROR;
-
 	if (s->check_type > XZ_CHECK_CRC32 && !IS_CRC64(s->check_type))
 		return XZ_UNSUPPORTED_CHECK;
 #else
@@ -604,6 +605,8 @@ static enum xz_ret dec_main(struct xz_dec *s, struct xz_buf *b)
 			if (ret != XZ_OK)
 				return ret;
 
+		/* Fall through */
+
 		case SEQ_BLOCK_START:
 			/* We need one byte of input to continue. */
 			if (b->in_pos == b->in_size)
@@ -627,6 +630,8 @@ static enum xz_ret dec_main(struct xz_dec *s, struct xz_buf *b)
 			s->temp.pos = 0;
 			s->sequence = SEQ_BLOCK_HEADER;
 
+		/* Fall through */
+
 		case SEQ_BLOCK_HEADER:
 			if (!fill_temp(s, b))
 				return XZ_OK;
@@ -637,6 +642,8 @@ static enum xz_ret dec_main(struct xz_dec *s, struct xz_buf *b)
 
 			s->sequence = SEQ_BLOCK_UNCOMPRESS;
 
+		/* Fall through */
+
 		case SEQ_BLOCK_UNCOMPRESS:
 			ret = dec_block(s, b);
 			if (ret != XZ_STREAM_END)
@@ -644,6 +651,8 @@ static enum xz_ret dec_main(struct xz_dec *s, struct xz_buf *b)
 
 			s->sequence = SEQ_BLOCK_PADDING;
 
+		/* Fall through */
+
 		case SEQ_BLOCK_PADDING:
 			/*
 			 * Size of Compressed Data + Block Padding
@@ -664,6 +673,8 @@ static enum xz_ret dec_main(struct xz_dec *s, struct xz_buf *b)
 
 			s->sequence = SEQ_BLOCK_CHECK;
 
+		/* Fall through */
+
 		case SEQ_BLOCK_CHECK:
 			if (s->check_type == XZ_CHECK_CRC32) {
 				ret = crc_validate(s, b, 32);
@@ -691,6 +702,8 @@ static enum xz_ret dec_main(struct xz_dec *s, struct xz_buf *b)
 
 			s->sequence = SEQ_INDEX_PADDING;
 
+		/* Fall through */
+
 		case SEQ_INDEX_PADDING:
 			while ((s->index.size + (b->in_pos - s->in_start))
 					& 3) {
@@ -713,6 +726,8 @@ static enum xz_ret dec_main(struct xz_dec *s, struct xz_buf *b)
 
 			s->sequence = SEQ_INDEX_CRC32;
 
+		/* Fall through */
+
 		case SEQ_INDEX_CRC32:
 			ret = crc_validate(s, b, 32);
 			if (ret != XZ_STREAM_END)
@@ -721,11 +736,17 @@ static enum xz_ret dec_main(struct xz_dec *s, struct xz_buf *b)
 			s->temp.size = STREAM_HEADER_SIZE;
 			s->sequence = SEQ_STREAM_FOOTER;
 
+		/* Fall through */
+
 		case SEQ_STREAM_FOOTER:
 			if (!fill_temp(s, b))
 				return XZ_OK;
 
 			return dec_stream_footer(s);
+
+		case SEQ_STREAM_PADDING:
+			/* Never reached, only silencing a warning */
+			break;
 		}
 	}
 
@@ -793,6 +814,79 @@ XZ_EXTERN enum xz_ret xz_dec_run(struct xz_dec *s, struct xz_buf *b)
 	return ret;
 }
 
+#ifdef XZ_DEC_CONCATENATED
+XZ_EXTERN enum xz_ret xz_dec_catrun(struct xz_dec *s, struct xz_buf *b,
+				    int finish)
+{
+	enum xz_ret ret;
+
+	if (DEC_IS_SINGLE(s->mode)) {
+		xz_dec_reset(s);
+		finish = true;
+	}
+
+	while (true) {
+		if (s->sequence == SEQ_STREAM_PADDING) {
+			/*
+			 * Skip Stream Padding. Its size must be a multiple
+			 * of four bytes which is tracked with s->pos.
+			 */
+			while (true) {
+				if (b->in_pos == b->in_size) {
+					/*
+					 * Note that if we are repeatedly
+					 * given no input and finish is false,
+					 * we will keep returning XZ_OK even
+					 * though no progress is being made.
+					 * The lack of XZ_BUF_ERROR support
+					 * isn't a problem here because a
+					 * reasonable caller will eventually
+					 * provide more input or set finish
+					 * to true.
+					 */
+					if (!finish)
+						return XZ_OK;
+
+					if (s->pos != 0)
+						return XZ_DATA_ERROR;
+
+					return XZ_STREAM_END;
+				}
+
+				if (b->in[b->in_pos] != 0x00) {
+					if (s->pos != 0)
+						return XZ_DATA_ERROR;
+
+					break;
+				}
+
+				++b->in_pos;
+				s->pos = (s->pos + 1) & 3;
+			}
+
+			/*
+			 * More input remains. It should be a new Stream.
+			 *
+			 * In single-call mode xz_dec_run() will always call
+			 * xz_dec_reset(). Thus, we need to do it here only
+			 * in multi-call mode.
+			 */
+			if (DEC_IS_MULTI(s->mode))
+				xz_dec_reset(s);
+		}
+
+		ret = xz_dec_run(s, b);
+
+		if (ret != XZ_STREAM_END)
+			break;
+
+		s->sequence = SEQ_STREAM_PADDING;
+	}
+
+	return ret;
+}
+#endif
+
 XZ_EXTERN struct xz_dec *xz_dec_init(enum xz_mode mode, uint32_t dict_max)
 {
 	struct xz_dec *s = kmalloc(sizeof(*s), GFP_KERNEL);
diff --git a/modules/xz-embedded/src/xz_lzma2.h b/modules/xz-embedded/src/xz_lzma2.h
index 071d67bee9..92d852d4f8 100644
--- a/modules/xz-embedded/src/xz_lzma2.h
+++ b/modules/xz-embedded/src/xz_lzma2.h
@@ -2,7 +2,7 @@
  * LZMA2 definitions
  *
  * Authors: Lasse Collin <lasse.collin@tukaani.org>
- *          Igor Pavlov <http://7-zip.org/>
+ *          Igor Pavlov <https://7-zip.org/>
  *
  * This file has been put into the public domain.
  * You can do whatever you want with this file.
diff --git a/modules/xz-embedded/src/xz_private.h b/modules/xz-embedded/src/xz_private.h
index 482b90f363..d9fd49b45f 100644
--- a/modules/xz-embedded/src/xz_private.h
+++ b/modules/xz-embedded/src/xz_private.h
@@ -37,6 +37,9 @@
 #		ifdef CONFIG_XZ_DEC_SPARC
 #			define XZ_DEC_SPARC
 #		endif
+#		ifdef CONFIG_XZ_DEC_MICROLZMA
+#			define XZ_DEC_MICROLZMA
+#		endif
 #		define memeq(a, b, size) (memcmp(a, b, size) == 0)
 #		define memzero(buf, size) memset(buf, 0, size)
 #	endif
diff --git a/modules/xz-embedded/src/xz_stream.h b/modules/xz-embedded/src/xz_stream.h
index 66cb5a7055..430bb3a0d1 100644
--- a/modules/xz-embedded/src/xz_stream.h
+++ b/modules/xz-embedded/src/xz_stream.h
@@ -19,7 +19,7 @@
 
 /*
  * See the .xz file format specification at
- * http://tukaani.org/xz/xz-file-format.txt
+ * https://tukaani.org/xz/xz-file-format.txt
  * to understand the container format.
  */
 
diff --git a/modules/xz-embedded/update.sh b/modules/xz-embedded/update.sh
index ecc1e3610e..37280bba12 100644
--- a/modules/xz-embedded/update.sh
+++ b/modules/xz-embedded/update.sh
@@ -4,11 +4,12 @@
 
 MY_TEMP_DIR=$(mktemp -d -t xz-embedded_update.XXXXXX) || exit 1
 
-git clone http://git.tukaani.org/xz-embedded.git ${MY_TEMP_DIR}/xz-embedded
+git clone https://git.tukaani.org/xz-embedded.git ${MY_TEMP_DIR}/xz-embedded
 
 COMMIT=$(git -C ${MY_TEMP_DIR}/xz-embedded rev-parse HEAD)
 cd $(dirname $0)
-perl -p -i -e "s/\[commit [0-9a-f]{40}\]/[${COMMIT}]/" README.mozilla;
+perl -p -i -e "s/\[[0-9a-f]{40}\]/[${COMMIT}]/" README.mozilla;
+rm -f README.mozilla.bak;
 
 rm -rf src
 mkdir src
@@ -23,7 +24,6 @@ mv ${MY_TEMP_DIR}/xz-embedded/linux/lib/xz/xz_dec_bcj.c src/
 mv ${MY_TEMP_DIR}/xz-embedded/linux/lib/xz/xz_dec_stream.c src/
 mv ${MY_TEMP_DIR}/xz-embedded/linux/lib/xz/xz_dec_lzma2.c src/
 rm -rf ${MY_TEMP_DIR}
-hg addremove src
 
 echo "###"
 echo "### Updated xz-embedded/src to $COMMIT."
diff --git a/netwerk/base/nsURLParsers.cpp b/netwerk/base/nsURLParsers.cpp
index b75ee0c4d4..ed4a216a88 100644
--- a/netwerk/base/nsURLParsers.cpp
+++ b/netwerk/base/nsURLParsers.cpp
@@ -4,6 +4,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include <string.h>
+#include <limits>
 
 #include "mozilla/RangedPtr.h"
 
diff --git a/python/mozbuild/mozbuild/mach_commands.py b/python/mozbuild/mozbuild/mach_commands.py
index bd3fbe921f..6a7b28810a 100644
--- a/python/mozbuild/mozbuild/mach_commands.py
+++ b/python/mozbuild/mozbuild/mach_commands.py
@@ -1137,8 +1137,13 @@ class Mar(MachCommandBase):
 
     @Command('mar', category='post-build',
         description='Create the mar file for the built product for distribution.')
-    def mar(self):
-        return self._run_make(directory="./tools/update-packaging/", target='', ensure_exit_code=False)
+    @CommandArgument('--bz2', action='store_true',
+        help='Compress the mar package with old-style bz2 instead of xz')
+    def mar(self, bz2):
+        if bz2:
+          return self._run_make(directory="./tools/update-packaging/", target='mar-package-bz2', ensure_exit_code=False)
+        else:
+          return self._run_make(directory="./tools/update-packaging/", target='mar-package', ensure_exit_code=False)
 
 @CommandProvider
 class Install(MachCommandBase):
diff --git a/toolkit/mozapps/installer/package-name.mk b/toolkit/mozapps/installer/package-name.mk
index 680590b3c5..548a93b47f 100644
--- a/toolkit/mozapps/installer/package-name.mk
+++ b/toolkit/mozapps/installer/package-name.mk
@@ -80,6 +80,7 @@ PKG_UPDATE_BASENAME = $(PKG_BASENAME)
 CHECKSUMS_FILE_BASENAME = $(PKG_BASENAME)
 MOZ_INFO_BASENAME = $(PKG_BASENAME)
 PKG_UPDATE_PATH = $(PKG_PATH)
+BARE_MAR = $(PKG_UPDATE_PATH)$(PKG_UPDATE_BASENAME).mar
 COMPLETE_MAR = $(PKG_UPDATE_PATH)$(PKG_UPDATE_BASENAME).complete.mar
 # PARTIAL_MAR needs to be processed by $(wildcard) before you use it.
 PARTIAL_MAR = $(PKG_UPDATE_PATH)$(PKG_UPDATE_BASENAME).partial.*.mar
diff --git a/toolkit/mozapps/update/common/errors.h b/toolkit/mozapps/update/common/errors.h
index 846118d55d..de1782b8e5 100644
--- a/toolkit/mozapps/update/common/errors.h
+++ b/toolkit/mozapps/update/common/errors.h
@@ -46,7 +46,7 @@
 #define WRITE_ERROR_ACCESS_DENIED 35
 // #define WRITE_ERROR_SHARING_VIOLATION 36 // Replaced with errors 46-48
 #define WRITE_ERROR_CALLBACK_APP 37
-#define UNEXPECTED_BZIP_ERROR 39
+#define UNEXPECTED_XZ_ERROR 39
 #define UNEXPECTED_MAR_ERROR 40
 #define UNEXPECTED_BSPATCH_ERROR 41
 #define UNEXPECTED_FILE_OPERATION_ERROR 42
diff --git a/toolkit/mozapps/update/updater/archivereader.cpp b/toolkit/mozapps/update/updater/archivereader.cpp
index 90cf45c3db..72debbe82e 100644
--- a/toolkit/mozapps/update/updater/archivereader.cpp
+++ b/toolkit/mozapps/update/updater/archivereader.cpp
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim:set ts=2 sw=2 sts=2 et cindent: */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
@@ -15,6 +14,9 @@
 #include "updatehelper.h"
 #endif
 
+#define XZ_USE_CRC64
+#include "xz.h"
+
 // These are generated at compile time based on the DER file for the channel
 // being used
 #ifdef MOZ_VERIFY_MAR_SIGNATURE
@@ -36,10 +38,10 @@
 # include <io.h>
 #endif
 
-static int inbuf_size  = 262144;
-static int outbuf_size = 262144;
-static char *inbuf  = nullptr;
-static char *outbuf = nullptr;
+static size_t inbuf_size  = 262144;
+static size_t outbuf_size = 262144;
+static uint8_t *inbuf  = nullptr;
+static uint8_t *outbuf = nullptr;
 
 /**
  * Performs a verification on the opened MAR file with the passed in
@@ -182,22 +184,22 @@ ArchiveReader::Open(const NS_tchar *path)
     Close();
 
   if (!inbuf) {
-    inbuf = (char *)malloc(inbuf_size);
+    inbuf = (uint8_t *)malloc(inbuf_size);
     if (!inbuf) {
       // Try again with a smaller buffer.
       inbuf_size = 1024;
-      inbuf = (char *)malloc(inbuf_size);
+      inbuf = (uint8_t *)malloc(inbuf_size);
       if (!inbuf)
         return ARCHIVE_READER_MEM_ERROR;
     }
   }
 
   if (!outbuf) {
-    outbuf = (char *)malloc(outbuf_size);
+    outbuf = (uint8_t *)malloc(outbuf_size);
     if (!outbuf) {
       // Try again with a smaller buffer.
       outbuf_size = 1024;
-      outbuf = (char *)malloc(outbuf_size);
+      outbuf = (uint8_t *)malloc(outbuf_size);
       if (!outbuf)
         return ARCHIVE_READER_MEM_ERROR;
     }
@@ -211,6 +213,9 @@ ArchiveReader::Open(const NS_tchar *path)
   if (!mArchive)
     return READ_ERROR;
 
+  xz_crc32_init();
+  xz_crc64_init();
+
   return OK;
 }
 
@@ -273,12 +278,21 @@ ArchiveReader::ExtractItemToStream(const MarItem *item, FILE *fp)
 {
   /* decompress the data chunk by chunk */
 
-  bz_stream strm;
-  int offset, inlen, outlen, ret = OK;
+  int offset, inlen, ret = OK;
+  struct xz_buf strm = { 0 };
+  enum xz_ret xz_rv = XZ_OK;
 
-  memset(&strm, 0, sizeof(strm));
-  if (BZ2_bzDecompressInit(&strm, 0, 0) != BZ_OK)
-    return UNEXPECTED_BZIP_ERROR;
+  struct xz_dec * dec = xz_dec_init(XZ_DYNALLOC, 64 * 1024 * 1024);
+  if (!dec) {
+    return UNEXPECTED_XZ_ERROR;
+  }
+
+  strm.in = inbuf;
+  strm.in_pos = 0;
+  strm.in_size = 0;
+  strm.out = outbuf;
+  strm.out_pos = 0;
+  strm.out_size = outbuf_size;
 
   offset = 0;
   for (;;) {
@@ -287,38 +301,50 @@ ArchiveReader::ExtractItemToStream(const MarItem *item, FILE *fp)
       break;
     }
 
-    if (offset < (int) item->length && strm.avail_in == 0) {
+    if (offset < (int) item->length && strm.in_pos == strm.in_size) {
       inlen = mar_read(mArchive, item, offset, inbuf, inbuf_size);
-      if (inlen <= 0)
-        return READ_ERROR;
+      if (inlen <= 0) {
+        ret = READ_ERROR;
+        break;
+      }
       offset += inlen;
-      strm.next_in = inbuf;
-      strm.avail_in = inlen;
+      strm.in_size = inlen;
+      strm.in_pos = 0;
     }
 
-    strm.next_out = outbuf;
-    strm.avail_out = outbuf_size;
+    xz_rv = xz_dec_run(dec, &strm);
 
-    ret = BZ2_bzDecompress(&strm);
-    if (ret != BZ_OK && ret != BZ_STREAM_END) {
-      ret = UNEXPECTED_BZIP_ERROR;
-      break;
-    }
-
-    outlen = outbuf_size - strm.avail_out;
-    if (outlen) {
-      if (fwrite(outbuf, outlen, 1, fp) != 1) {
+    if (strm.out_pos == outbuf_size) {
+      if (fwrite(outbuf, 1, strm.out_pos, fp) != strm.out_pos) {
         ret = WRITE_ERROR_EXTRACT;
         break;
       }
+
+      strm.out_pos = 0;
     }
 
-    if (ret == BZ_STREAM_END) {
-      ret = OK;
+    if (xz_rv == XZ_OK) {
+      // There is still more data to decompress.
+      continue;
+    }
+
+    // The return value of xz_dec_run is not XZ_OK and if it isn't XZ_STREAM_END
+    // an error has occured.
+    if (xz_rv != XZ_STREAM_END) {
+      ret = UNEXPECTED_XZ_ERROR;
       break;
     }
+
+    // Write out the remainder of the decompressed data. In the case of
+    // strm.out_pos == 0 this is needed to create empty files included in the
+    // mar file.
+    if (fwrite(outbuf, 1, strm.out_pos, fp) != strm.out_pos) {
+      ret = WRITE_ERROR_EXTRACT;
+    }
+
+    break;
   }
 
-  BZ2_bzDecompressEnd(&strm);
+  xz_dec_end(dec);
   return ret;
 }
diff --git a/toolkit/mozapps/update/updater/updater-common.build b/toolkit/mozapps/update/updater/updater-common.build
index a46c1388cc..1ace8fcc71 100644
--- a/toolkit/mozapps/update/updater/updater-common.build
+++ b/toolkit/mozapps/update/updater/updater-common.build
@@ -57,6 +57,7 @@ else:
 
 USE_LIBS += [
     'mar',
+    'xz-embedded',
 ]
 
 if CONFIG['MOZ_SYSTEM_BZ2']:
diff --git a/tools/update-packaging/Makefile.in b/tools/update-packaging/Makefile.in
index 4788a55752..a751ae3ce5 100644
--- a/tools/update-packaging/Makefile.in
+++ b/tools/update-packaging/Makefile.in
@@ -31,7 +31,7 @@ MAR_BIN	= $(DIST)/host/bin/mar$(HOST_BIN_SUFFIX)
 MBSDIFF_BIN	= $(DIST)/host/bin/mbsdiff$(HOST_BIN_SUFFIX)
 
 OVERRIDE_DEFAULT_GOAL := full-update
-full-update:: complete-patch
+full-update:: mar-package
 
 ifeq ($(OS_TARGET), WINNT)
 ifdef AB_CD
@@ -70,3 +70,23 @@ partial-patch:: $(dir-stage)
 ifdef MOZ_SIGN_CMD
 	$(MOZ_SIGN_CMD) -f mar '$(STAGE_DIR)/$(PKG_UPDATE_BASENAME).partial.$(SRC_BUILD_ID)-$(DST_BUILD_ID).mar'
 endif
+
+mar-package: $(call mkdir_deps,$(ABS_DIST)/$(PKG_STAGE_DIR))
+	@echo 'Creating update mar (xz compressed)...'
+	MAR=$(MAR_BIN) \
+	  $(srcdir)/make_full_update.sh \
+	  '$(DIST)/$(BARE_MAR)' \
+	  '$(PACKAGE_DIR)'
+ifdef MOZ_SIGN_CMD
+	$(MOZ_SIGN_CMD) -f mar '$(DIST)/$(BARE_MAR)'
+endif
+
+mar-package-bz2: $(call mkdir_deps,$(ABS_DIST)/$(PKG_STAGE_DIR))
+	@echo 'Creating update mar (bz2 compressed)...'
+	MAR_OLD_FORMAT=1 MAR=$(MAR_BIN) \
+	  $(srcdir)/make_full_update.sh \
+	  '$(DIST)/$(COMPLETE_MAR)' \
+	  '$(PACKAGE_DIR)'
+ifdef MOZ_SIGN_CMD
+	$(MOZ_SIGN_CMD) -f mar '$(DIST)/$(COMPLETE_MAR)'
+endif
\ No newline at end of file
diff --git a/tools/update-packaging/common.sh b/tools/update-packaging/common.sh
index 24f1ca6eb4..3df2cc4768 100644
--- a/tools/update-packaging/common.sh
+++ b/tools/update-packaging/common.sh
@@ -9,10 +9,15 @@
 #
 
 # -----------------------------------------------------------------------------
-# By default just assume that these tools exist on our path
+# By default just assume that these tools exist in our path
 MAR=${MAR:-mar}
-BZIP2=${BZIP2:-bzip2}
 MBSDIFF=${MBSDIFF:-mbsdiff}
+if [[ -z "${MAR_OLD_FORMAT}" ]]; then
+  XZ=${XZ:-xz}
+else
+  MAR_OLD_FORMAT=1
+  BZIP2=${BZIP2:-bzip2}
+fi
 
 # -----------------------------------------------------------------------------
 # Helper routines
diff --git a/tools/update-packaging/make_full_update.sh b/tools/update-packaging/make_full_update.sh
index ba1404474f..c480f8ee66 100644
--- a/tools/update-packaging/make_full_update.sh
+++ b/tools/update-packaging/make_full_update.sh
@@ -93,7 +93,11 @@ for ((i=0; $i<$num_files; i=$i+1)); do
 
   dir=$(dirname "$f")
   mkdir -p "$workdir/$dir"
-  $BZIP2 -cz9 "$targetdir/$f" > "$workdir/$f"
+  if [[ -n $MAR_OLD_FORMAT ]]; then
+    $BZIP2 -cz9 "$targetdir/$f" > "$workdir/$f"
+  else
+    $XZ --compress --x86 --lzma2 --format=xz --check=crc64 --force --stdout "$targetdir/$f" > "$workdir/$f"
+  fi
   copy_perm "$targetdir/$f" "$workdir/$f"
 
   targetfiles="$targetfiles \"$f\""
@@ -104,8 +108,13 @@ notice ""
 notice "Adding file and directory remove instructions from file 'removed-files'"
 append_remove_instructions "$targetdir" "$updatemanifestv2" "$updatemanifestv3"
 
-$BZIP2 -z9 "$updatemanifestv2" && mv -f "$updatemanifestv2.bz2" "$updatemanifestv2"
-$BZIP2 -z9 "$updatemanifestv3" && mv -f "$updatemanifestv3.bz2" "$updatemanifestv3"
+if [[ -n $MAR_OLD_FORMAT ]]; then
+  $BZIP2 -z9 "$updatemanifestv2" && mv -f "$updatemanifestv2.bz2" "$updatemanifestv2"
+  $BZIP2 -z9 "$updatemanifestv3" && mv -f "$updatemanifestv3.bz2" "$updatemanifestv3"
+else
+  $XZ --compress --x86 --lzma2 --format=xz --check=crc64 --force "$updatemanifestv2" && mv -f "$updatemanifestv2.xz" "$updatemanifestv2"
+  $XZ --compress --x86 --lzma2 --format=xz --check=crc64 --force "$updatemanifestv3" && mv -f "$updatemanifestv3.xz" "$updatemanifestv3"
+fi
 
 eval "$MAR -C \"$workdir\" -c output.mar $targetfiles"
 mv -f "$workdir/output.mar" "$archive"
diff --git a/tools/update-packaging/make_incremental_update.sh b/tools/update-packaging/make_incremental_update.sh
index 90372c017e..af3af854fd 100644
--- a/tools/update-packaging/make_incremental_update.sh
+++ b/tools/update-packaging/make_incremental_update.sh
@@ -169,7 +169,11 @@ for ((i=0; $i<$num_oldfiles; i=$i+1)); do
     if check_for_add_if_not_update "$f"; then
       # The full workdir may not exist yet, so create it if necessary.
       mkdir -p `dirname "$workdir/$f"`
-      $BZIP2 -cz9 "$newdir/$f" > "$workdir/$f"
+      if [[ -n $MAR_OLD_FORMAT ]]; then
+        $BZIP2 -cz9 "$newdir/$f" > "$workdir/$f"
+      else
+        $XZ --compress --x86 --lzma2 --format=xz --check=crc64 --force --stdout "$newdir/$f" > "$workdir/$f"
+      fi
       copy_perm "$newdir/$f" "$workdir/$f"
       make_add_if_not_instruction "$f" "$updatemanifestv3"
       archivefiles="$archivefiles \"$f\""
@@ -179,7 +183,11 @@ for ((i=0; $i<$num_oldfiles; i=$i+1)); do
     if check_for_forced_update "$requested_forced_updates" "$f"; then
       # The full workdir may not exist yet, so create it if necessary.
       mkdir -p `dirname "$workdir/$f"`
-      $BZIP2 -cz9 "$newdir/$f" > "$workdir/$f"
+      if [[ -n $MAR_OLD_FORMAT ]]; then
+        $BZIP2 -cz9 "$newdir/$f" > "$workdir/$f"
+      else
+        $XZ --compress --x86 --lzma2 --format=xz --check=crc64 --force --stdout "$newdir/$f" > "$workdir/$f"
+      fi
       copy_perm "$newdir/$f" "$workdir/$f"
       make_add_instruction "$f" "$updatemanifestv2" "$updatemanifestv3" 1
       archivefiles="$archivefiles \"$f\""
@@ -207,21 +215,44 @@ for ((i=0; $i<$num_oldfiles; i=$i+1)); do
       # if service is not enabled then default to old behavior
       if [ -z "$MBSDIFF_HOOK" ]; then
         $MBSDIFF "$olddir/$f" "$newdir/$f" "$workdir/$f.patch"
-        $BZIP2 -z9 "$workdir/$f.patch"
+        if [[ -n $MAR_OLD_FORMAT ]]; then
+          $BZIP2 -z9 "$workdir/$f.patch"
+        else
+          $XZ --compress --x86 --lzma2 --format=xz --check=crc64 --force "$workdir/$f.patch"
+        fi
       else
         # if service enabled then check patch existence for retrieval
-        if $MBSDIFF_HOOK -g "$olddir/$f" "$newdir/$f" "$workdir/$f.patch.bz2"; then
-          notice "file \"$f\" found in funsize, diffing skipped"
+        if [[ -n $MAR_OLD_FORMAT ]]; then
+          if $MBSDIFF_HOOK -g "$olddir/$f" "$newdir/$f" "$workdir/$f.patch.bz2"; then
+            notice "file \"$f\" found in funsize, diffing skipped"
+          else
+            # if not found already - compute it and cache it for future use
+            $MBSDIFF "$olddir/$f" "$newdir/$f" "$workdir/$f.patch"
+            $BZIP2 -z9 "$workdir/$f.patch"
+            $MBSDIFF_HOOK -u "$olddir/$f" "$newdir/$f" "$workdir/$f.patch.bz2"
+          fi
         else
-          # if not found already - compute it and cache it for future use
-          $MBSDIFF "$olddir/$f" "$newdir/$f" "$workdir/$f.patch"
-          $BZIP2 -z9 "$workdir/$f.patch"
-          $MBSDIFF_HOOK -u "$olddir/$f" "$newdir/$f" "$workdir/$f.patch.bz2"
+          if $MBSDIFF_HOOK -g "$olddir/$f" "$newdir/$f" "$workdir/$f.patch.xz"; then
+            notice "file \"$f\" found in funsize, diffing skipped"
+          else
+            # if not found already - compute it and cache it for future use
+            $MBSDIFF "$olddir/$f" "$newdir/$f" "$workdir/$f.patch"
+            $XZ --compress --x86 --lzma2 --format=xz --check=crc64 --force "$workdir/$f.patch"
+            $MBSDIFF_HOOK -u "$olddir/$f" "$newdir/$f" "$workdir/$f.patch.xz"
+          fi
         fi
       fi
-      $BZIP2 -cz9 "$newdir/$f" > "$workdir/$f"
+      if [[ -n $MAR_OLD_FORMAT ]]; then
+        $BZIP2 -cz9 "$newdir/$f" > "$workdir/$f"
+      else
+        $XZ --compress --x86 --lzma2 --format=xz --check=crc64 --force --stdout "$newdir/$f" > "$workdir/$f"
+      fi
       copy_perm "$newdir/$f" "$workdir/$f"
-      patchfile="$workdir/$f.patch.bz2"
+      if [[ -n $MAR_OLD_FORMAT ]]; then
+        patchfile="$workdir/$f.patch.bz2"
+      else
+        patchfile="$workdir/$f.patch.xz"
+      fi
       patchsize=$(get_file_size "$patchfile")
       fullsize=$(get_file_size "$workdir/$f")
 
@@ -262,7 +293,11 @@ for ((i=0; $i<$num_newfiles; i=$i+1)); do
   dir=$(dirname "$workdir/$f")
   mkdir -p "$dir"
 
-  $BZIP2 -cz9 "$newdir/$f" > "$workdir/$f"
+  if [[ -n $MAR_OLD_FORMAT ]]; then
+    $BZIP2 -cz9 "$newdir/$f" > "$workdir/$f"
+  else
+    $XZ --compress --x86 --lzma2 --format=xz --check=crc64 --force --stdout "$newdir/$f" > "$workdir/$f"
+  fi
   copy_perm "$newdir/$f" "$workdir/$f"
 
   if check_for_add_if_not_update "$f"; then
@@ -303,8 +338,13 @@ for ((i=0; $i<$num_olddirs; i=$i+1)); do
   fi
 done
 
-$BZIP2 -z9 "$updatemanifestv2" && mv -f "$updatemanifestv2.bz2" "$updatemanifestv2"
-$BZIP2 -z9 "$updatemanifestv3" && mv -f "$updatemanifestv3.bz2" "$updatemanifestv3"
+if [[ -n $MAR_OLD_FORMAT ]]; then
+  $BZIP2 -z9 "$updatemanifestv2" && mv -f "$updatemanifestv2.bz2" "$updatemanifestv2"
+  $BZIP2 -z9 "$updatemanifestv3" && mv -f "$updatemanifestv3.bz2" "$updatemanifestv3"
+else
+  $XZ --compress --x86 --lzma2 --format=xz --check=crc64 --force "$updatemanifestv2" && mv -f "$updatemanifestv2.xz" "$updatemanifestv2"
+  $XZ --compress --x86 --lzma2 --format=xz --check=crc64 --force "$updatemanifestv3" && mv -f "$updatemanifestv3.xz" "$updatemanifestv3"
+fi
 
 mar_command="$MAR"
 if [[ -n $MOZ_PRODUCT_VERSION ]]
diff --git a/tools/update-packaging/make_incremental_updates.py b/tools/update-packaging/make_incremental_updates.py
index d346ee2df0..dc7b3a01ea 100644
--- a/tools/update-packaging/make_incremental_updates.py
+++ b/tools/update-packaging/make_incremental_updates.py
@@ -4,7 +4,7 @@
 
 import os
 import shutil
-import sha
+import hashlib
 from os.path import join, getsize
 from stat import *
 import re
@@ -12,9 +12,9 @@ import sys
 import getopt
 import time
 import datetime
-import bz2
 import string
 import tempfile
+import io
 
 class PatchInfo:
     """ Represents the meta-data associated with a patch
@@ -107,23 +107,23 @@ class PatchInfo:
         """ Create the v2 manifest file in the root of the work_dir """
         manifest_file_path = os.path.join(self.work_dir,"updatev2.manifest")
         manifest_file = open(manifest_file_path, "wb")
-        manifest_file.writelines("type \"partial\"\n")
-        manifest_file.writelines(string.join(self.manifestv2, '\n'))
-        manifest_file.writelines("\n")
+        manifest_file.writelines(io.BytesIO(b"type \"partial\"\n"))
+        manifest_file.writelines(io.BytesIO('\n'.join(self.manifestv2).encode('ascii')))
+        manifest_file.writelines(io.BytesIO(b"\n"))
         manifest_file.close()
 
-        bzip_file(manifest_file_path)
+        xz_file(manifest_file_path)
         self.archive_files.append('"updatev2.manifest"')
 
         """ Create the v3 manifest file in the root of the work_dir """
         manifest_file_path = os.path.join(self.work_dir,"updatev3.manifest")
         manifest_file = open(manifest_file_path, "wb")
-        manifest_file.writelines("type \"partial\"\n")
-        manifest_file.writelines(string.join(self.manifestv3, '\n'))
-        manifest_file.writelines("\n")
+        manifest_file.writelines(io.BytesIO(b"type \"partial\"\n"))
+        manifest_file.writelines(io.BytesIO('\n'.join(self.manifestv3).encode('ascii')))
+        manifest_file.writelines(io.BytesIO(b"\n"))
         manifest_file.close()
 
-        bzip_file(manifest_file_path)
+        xz_file(manifest_file_path)
         self.archive_files.append('"updatev3.manifest"')
 
     def build_marfile_entry_hash(self, root_path):
@@ -176,8 +176,8 @@ class MarFileEntry:
 
     def calc_file_sha_digest(self, filename):
         """ Returns sha digest of given filename"""
-        file_content = open(filename, 'r').read()
-        return sha.new(file_content).digest()
+        file_content = open(filename, 'rb').read()
+        return hashlib.sha1(file_content).digest()
 
     def sha(self):
         """ Returns sha digest of file repreesnted by this _marfile_entry"""
@@ -188,7 +188,7 @@ class MarFileEntry:
 def exec_shell_cmd(cmd):
     """Execs shell cmd and raises an exception if the cmd fails"""
     if (os.system(cmd)):
-        raise Exception, "cmd failed "+cmd
+        raise Exception("cmd failed "+cmd)
 
 
 def copy_file(src_file_abs_path, dst_file_abs_path):
@@ -199,19 +199,19 @@ def copy_file(src_file_abs_path, dst_file_abs_path):
     # Copy the file over
     shutil.copy2(src_file_abs_path, dst_file_abs_path)
 
-def bzip_file(filename):
-    """ Bzip's the file in place.  The original file is replaced with a bzip'd version of itself
+def xz_file(filename):
+    """ XZ compresses the file in place.  The original file is replaced with the xz compressed version of itself
         assumes the path is absolute"""
-    exec_shell_cmd('bzip2 -z9 "' + filename+'"')
-    os.rename(filename+".bz2",filename)
+    exec_shell_cmd('xz --compress --x86 --lzma2 --format=xz --check=crc64 "' + filename+'"')
+    os.rename(filename+".xz",filename)
 
-def bunzip_file(filename):
-    """ Bzip's the file in palce.   The original file is replaced with a bunzip'd version of itself.
-        doesn't matter if the filename ends in .bz2 or not"""
-    if not filename.endswith(".bz2"):
-        os.rename(filename, filename+".bz2")
-        filename=filename+".bz2"
-    exec_shell_cmd('bzip2 -d "' + filename+'"')
+def xzunzip_file(filename):
+    """ xz decompresses the file in palce.  The original file is replaced with a xz decompressed version of itself.
+        doesn't matter if the filename ends in .xz or not"""
+    if not filename.endswith(".xz"):
+        os.rename(filename, filename+".xz")
+        filename=filename+".xz"
+    exec_shell_cmd('xz -d "' + filename+'"')
 
 
 def extract_mar(filename, work_dir):
@@ -241,14 +241,14 @@ def create_partial_patch_for_file(from_marfile_entry, to_marfile_entry, shas, pa
         if not os.path.exists(patch_file_dir):
             os.makedirs(patch_file_dir)
 
-        # Create bzip'd patch file
+        # Create xz'd patch file
         exec_shell_cmd("mbsdiff "+from_marfile_entry.abs_path+" "+to_marfile_entry.abs_path+" "+patch_file_abs_path)
-        bzip_file(patch_file_abs_path)
+        xz_file(patch_file_abs_path)
 
-        # Create bzip's full file
+        # Create xz full file
         full_file_abs_path =  os.path.join(patch_info.work_dir, to_marfile_entry.name)
         shutil.copy2(to_marfile_entry.abs_path, full_file_abs_path)
-        bzip_file(full_file_abs_path)
+        xz_file(full_file_abs_path)
 
         if os.path.getsize(patch_file_abs_path) < os.path.getsize(full_file_abs_path):
             # Patch is smaller than file.  Remove the file and add patch to manifest
@@ -304,13 +304,17 @@ def process_explicit_remove_files(dir_path, patch_info):
         list_file_path = os.path.join(dir_path, "Contents/Resources/removed-files")
 
     if (os.path.exists(list_file_path)):
-        list_file = bz2.BZ2File(list_file_path,"r") # throws if doesn't exist
+        fd, tmppath = tempfile.mkstemp('', 'tmp', os.getcwd())
+        os.close(fd)
+        exec_shell_cmd('xz -k -d --stdout "' + list_file_path + '" > "'+tmppath+'"')
+        list_file = open(tmppath)
 
         lines = []
         for line in list_file:
             lines.append(line.strip())
-        list_file.close()
 
+        list_file.close()
+        os.remove(tmppath)
         lines.sort(reverse=True)
         for line in lines:
             # Exclude any blank and comment lines.
@@ -406,7 +410,7 @@ def create_partial_patch(from_dir_path, to_dir_path, patch_filename, shas, patch
     patch_info.create_manifest_files()
 
     # And construct the mar
-    mar_cmd = 'mar -C '+patch_info.work_dir+' -c output.mar '+string.join(patch_info.archive_files, ' ')
+    mar_cmd = 'mar -C '+patch_info.work_dir+' -c output.mar '+' '.join(patch_info.archive_files)
     exec_shell_cmd(mar_cmd)
 
     # Copy mar to final destination
@@ -431,11 +435,18 @@ def get_buildid(work_dir):
             print 'WARNING: application.ini not found, cannot find build ID'
             return ''
 
-    file = bz2.BZ2File(ini)
+    fd, tmppath = tempfile.mkstemp('', 'tmp', os.getcwd())
+    os.close(fd)
+    exec_shell_cmd('xz -k -d --stdout "' + ini + '" > "'+tmppath+'"')
+    file = open(tmppath)
     for line in file:
         if line.find('BuildID') == 0:
+            file.close()
+            os.remove(tmppath)
             return line.strip().split('=')[1]
-    print 'WARNING: cannot find build ID in application.ini'
+    print('WARNING: cannot find build ID in application.ini')
+    file.close()
+    os.remove(tmppath)
     return ''
 
 def decode_filename(filepath):
@@ -486,7 +497,7 @@ def create_partial_patches(patches):
             extract_mar(from_filename,work_dir_from)
             from_decoded = decode_filename(from_filename)
             from_buildid = get_buildid(work_dir_from)
-            from_shasum = sha.sha(open(from_filename).read()).hexdigest()
+            from_shasum = hashlib.sha1(open(from_filename, "rb").read()).hexdigest()
             from_size = str(os.path.getsize(to_filename))
 
             # Extract to mar into to dir
@@ -495,14 +506,14 @@ def create_partial_patches(patches):
             extract_mar(to_filename, work_dir_to)
             to_decoded = decode_filename(from_filename)
             to_buildid = get_buildid(work_dir_to)
-            to_shasum = sha.sha(open(to_filename).read()).hexdigest()
+            to_shasum = hashlib.sha1(open(to_filename, 'rb').read()).hexdigest()
             to_size = str(os.path.getsize(to_filename))
 
             mar_extract_time = time.time()
 
             partial_filename = create_partial_patch(work_dir_from, work_dir_to, patch_filename, shas, PatchInfo(work_dir, ['update.manifest','updatev2.manifest','updatev3.manifest'],[]),forced_updates,['channel-prefs.js','update-settings.ini'])
             partial_buildid = to_buildid
-            partial_shasum = sha.sha(open(partial_filename).read()).hexdigest()
+            partial_shasum = hashlib.sha1(open(partial_filename, "rb").read()).hexdigest()
             partial_size = str(os.path.getsize(partial_filename))
 
             metadata.append({
diff --git a/tools/update-packaging/test/catmanifest.sh b/tools/update-packaging/test/catmanifest.sh
index 354c3ff411..e6349d47a3 100644
--- a/tools/update-packaging/test/catmanifest.sh
+++ b/tools/update-packaging/test/catmanifest.sh
@@ -9,6 +9,6 @@ mkdir -p "$workdir"
 cp "$1" "$workdir"
 cd "$workdir"
 mar -x "$1"
-mv updatev2.manifest updatev2.manifest.bz2
-bzip2 -d updatev2.manifest.bz2
+mv updatev2.manifest updatev2.manifest.xz
+xz -d updatev2.manifest.xz
 cat updatev2.manifest
diff --git a/tools/update-packaging/test/common.sh b/tools/update-packaging/test/common.sh
index 7c133724e5..a9c904f037 100644
--- a/tools/update-packaging/test/common.sh
+++ b/tools/update-packaging/test/common.sh
@@ -10,9 +10,9 @@
 # In here to use the local common.sh to allow the full mars to have unfiltered files
 
 # -----------------------------------------------------------------------------
-# By default just assume that these tools exist on our path
+# By default just assume that these tools exist in our path
 MAR=${MAR:-mar}
-BZIP2=${BZIP2:-bzip2}
+XZ=${XZ:-xz}
 MBSDIFF=${MBSDIFF:-mbsdiff}
 
 # -----------------------------------------------------------------------------
diff --git a/tools/update-packaging/test/diffmar.sh b/tools/update-packaging/test/diffmar.sh
index 771b6b0ce1..f1dfc7fbdd 100644
--- a/tools/update-packaging/test/diffmar.sh
+++ b/tools/update-packaging/test/diffmar.sh
@@ -30,19 +30,19 @@ cp "$2" "$todir"
 cd "$fromdir"
 mar -x "$1"
 rm "$1"
-mv updatev2.manifest updatev2.manifest.bz2
-bzip2 -d updatev2.manifest.bz2
-mv updatev3.manifest updatev3.manifest.bz2
-bzip2 -d updatev3.manifest.bz2
+mv updatev2.manifest updatev2.manifest.xz
+xz -d updatev2.manifest.xz
+mv updatev3.manifest updatev3.manifest.xz
+xz -d updatev3.manifest.xz
 ls $lsargs > files.txt
 
 cd "$todir"
 mar -x "$2"
 rm "$2"
-mv updatev2.manifest updatev2.manifest.bz2
-bzip2 -d updatev2.manifest.bz2
-mv updatev3.manifest updatev3.manifest.bz2
-bzip2 -d updatev3.manifest.bz2
+mv updatev2.manifest updatev2.manifest.xz
+xz -d updatev2.manifest.xz
+mv updatev3.manifest updatev3.manifest.xz
+xz -d updatev3.manifest.xz
 ls $lsargs > files.txt
 
 echo "diffing $fromdir and $todir"
diff --git a/tools/update-packaging/test/make_full_update.sh b/tools/update-packaging/test/make_full_update.sh
index f2907da9ee..d6a01dcb76 100644
--- a/tools/update-packaging/test/make_full_update.sh
+++ b/tools/update-packaging/test/make_full_update.sh
@@ -94,7 +94,7 @@ for ((i=0; $i<$num_files; i=$i+1)); do
 
   dir=$(dirname "$f")
   mkdir -p "$workdir/$dir"
-  $BZIP2 -cz9 "$targetdir/$f" > "$workdir/$f"
+  $XZ --compress --x86 --lzma2 --format=xz --check=crc64 --force --stdout "$targetdir/$f" > "$workdir/$f"
   copy_perm "$targetdir/$f" "$workdir/$f"
 
   targetfiles="$targetfiles \"$f\""
@@ -105,8 +105,8 @@ notice ""
 notice "Adding file and directory remove instructions from file 'removed-files'"
 append_remove_instructions "$targetdir" "$updatemanifestv2" "$updatemanifestv3"
 
-$BZIP2 -z9 "$updatemanifestv2" && mv -f "$updatemanifestv2.bz2" "$updatemanifestv2"
-$BZIP2 -z9 "$updatemanifestv3" && mv -f "$updatemanifestv3.bz2" "$updatemanifestv3"
+$XZ --compress --x86 --lzma2 --format=xz --check=crc64 --force "$updatemanifestv2" && mv -f "$updatemanifestv2.xz" "$updatemanifestv2"
+$XZ --compress --x86 --lzma2 --format=xz --check=crc64 --force "$updatemanifestv3" && mv -f "$updatemanifestv3.xz" "$updatemanifestv3"
 
 eval "$MAR -C \"$workdir\" -c output.mar $targetfiles"
 mv -f "$workdir/output.mar" "$archive"
diff --git a/tools/update-packaging/unwrap_full_update.pl b/tools/update-packaging/unwrap_full_update.pl
index ead1157db9..90aa8ee726 100644
--- a/tools/update-packaging/unwrap_full_update.pl
+++ b/tools/update-packaging/unwrap_full_update.pl
@@ -13,7 +13,7 @@
 
 use Getopt::Std;
 
-my ($MAR, $BZIP2, $archive, @marentries, @marfiles);
+my ($MAR, $XZ, $BZIP2, $MAR_OLD_FORMAT, $archive, @marentries, @marfiles);
 
 if (defined($ENV{"MAR"})) {
     $MAR = $ENV{"MAR"};
@@ -29,6 +29,18 @@ else {
     $BZIP2 = "bzip2";
 }
 
+if (defined($ENV{"XZ"})) {
+    $XZ = $ENV{"XZ"};
+}
+else {
+    if (system("xz --version > /dev/null 2>&1") != 0) {
+        die("The xz executable must be in the path.");
+    }
+    else {
+        $XZ = "xz";
+    }
+}
+
 sub print_usage
 {
     print "Usage: unwrap_full_update.pl [OPTIONS] ARCHIVE\n\n";
@@ -50,18 +62,43 @@ $archive = $ARGV[0];
 
 $? && die("Couldn't run \"$MAR\" -t");
 
-shift @marentries;
+if (system("$MAR -x \"$archive\"") != 0) {
+  die "Couldn't run $MAR -x";
+}
 
-system("$MAR -x \"$archive\"") == 0 || die "Couldn't run $MAR -x";
+# Try to determine if the mar file contains bzip2 compressed files and if not
+# assume that the mar file contains lzma compressed files. The updatev3.manifest
+# file is checked since a valid mar file must have this file in the root path.
+open(my $testfilename, "updatev3.manifest") or die $!;
+binmode($testfilename);
+read($testfilename, my $bytes, 3);
+if ($bytes eq "BZh") {
+    $MAR_OLD_FORMAT = 1;
+} else {
+    undef $MAR_OLD_FORMAT;
+}
+close $testfilename;
+
+shift @marentries;
 
 foreach (@marentries) {
     tr/\n\r//d;
     my @splits = split(/\t/,$_);
     my $file = $splits[2];
 
-    system("mv \"$file\" \"$file.bz2\"") == 0 ||
-      die "Couldn't mv \"$file\"";
-    system("\"$BZIP2\" -d \"$file.bz2\"") == 0 ||
-      die "Couldn't decompress \"$file\"";
+    print "Decompressing: " . $file . "\n";
+    if ($MAR_OLD_FORMAT == 1) {
+      system("mv \"$file\" \"$file.bz2\"") == 0 ||
+        die "Couldn't mv \"$file\"";
+      system("\"$BZIP2\" -d \"$file.bz2\"") == 0 ||
+        die "Couldn't decompress \"$file\"";
+    }
+    else {
+      system("mv \"$file\" \"$file.xz\"") == 0 ||
+        die "Couldn't mv \"$file\"";
+      system("\"$XZ\" -d \"$file.xz\"") == 0 ||
+        die "Couldn't decompress \"$file\"";
+    }
 }
 
+print "Finished\n";