diff --git a/dom/bindings/RootedOwningNonNull.h b/dom/bindings/RootedOwningNonNull.h
index 13424d1557..387a707344 100644
--- a/dom/bindings/RootedOwningNonNull.h
+++ b/dom/bindings/RootedOwningNonNull.h
@@ -50,21 +50,12 @@ struct GCPolicy<mozilla::OwningNonNull<T>>
 } // namespace JS
 
 namespace js {
-template<typename T>
-struct RootedBase<mozilla::OwningNonNull<T>>
+template<typename T, typename Wrapper>
+struct WrappedPtrOperations<mozilla::OwningNonNull<T>, Wrapper>
 {
-  typedef mozilla::OwningNonNull<T> SmartPtrType;
-
-  operator SmartPtrType& () const
-  {
-    auto& self = *static_cast<const JS::Rooted<SmartPtrType>*>(this);
-    return self.get();
-  }
-
   operator T& () const
   {
-    auto& self = *static_cast<const JS::Rooted<SmartPtrType>*>(this);
-    return self.get();
+    return static_cast<const Wrapper*>(this)->get();
   }
 };
 } // namespace js
diff --git a/dom/bindings/RootedRefPtr.h b/dom/bindings/RootedRefPtr.h
index 34f2da5c9f..2563d46493 100644
--- a/dom/bindings/RootedRefPtr.h
+++ b/dom/bindings/RootedRefPtr.h
@@ -38,19 +38,12 @@ struct GCPolicy<RefPtr<T>>
 } // namespace JS
 
 namespace js {
-template<typename T>
-struct RootedBase<RefPtr<T>>
+template<typename T, typename Wrapper>
+struct WrappedPtrOperations<RefPtr<T>, Wrapper>
 {
-  operator RefPtr<T>& () const
-  {
-    auto& self = *static_cast<const JS::Rooted<RefPtr<T>>*>(this);
-    return self.get();
-  }
-
   operator T*() const
   {
-    auto& self = *static_cast<const JS::Rooted<RefPtr<T>>*>(this);
-    return self.get();
+    return static_cast<const Wrapper*>(this)->get();
   }
 };
 } // namespace js
diff --git a/dom/events/DataTransfer.cpp b/dom/events/DataTransfer.cpp
index 5e7d477dfb..3a3f5464d2 100644
--- a/dom/events/DataTransfer.cpp
+++ b/dom/events/DataTransfer.cpp
@@ -639,16 +639,11 @@ DataTransfer::PrincipalMaySetData(const nsAString& aType,
       return false;
     }
 
-    if (aType.EqualsASCII(kFileMime) ||
-        aType.EqualsASCII(kFilePromiseMime)) {
-      NS_WARNING("Disallowing adding x-moz-file or x-moz-file-promize types to DataTransfer");
-      return false;
-    }
-    
-    // Disallow content from creating x-moz-place flavors, so that it cannot
-    // create fake Places smart queries exposing user data.
-    if (StringBeginsWith(aType, NS_LITERAL_STRING("text/x-moz-place"))) {
-      NS_WARNING("Disallowing adding moz-place types to DataTransfer");
+    // Don't allow adding internal types of the form */x-moz-*, but
+    // special-case the url types as they are simple variations of urls.
+    if (FindInReadable(NS_LITERAL_STRING(kInternal_Mimetype_Prefix), aType) &&
+        !StringBeginsWith(aType, NS_LITERAL_STRING("text/x-moz-url"))) {
+      NS_WARNING("Disallowing adding requested internal type to DataTransfer");
       return false;
     }
   }
diff --git a/dom/plugins/base/nsJSNPRuntime.cpp b/dom/plugins/base/nsJSNPRuntime.cpp
index 1d42c18d64..7a118cae35 100644
--- a/dom/plugins/base/nsJSNPRuntime.cpp
+++ b/dom/plugins/base/nsJSNPRuntime.cpp
@@ -1747,7 +1747,7 @@ NPObjWrapper_ObjectMoved(JSObject *obj, const JSObject *old)
   auto entry =
     static_cast<NPObjWrapperHashEntry*>(sNPObjWrappers->Search(npobj));
   MOZ_ASSERT(entry && entry->mJSObj);
-  MOZ_ASSERT(entry->mJSObj.unbarrieredGetPtr() == old);
+  MOZ_ASSERT(entry->mJSObj == old);
   entry->mJSObj = obj;
 }
 
diff --git a/dom/xbl/nsXBLMaybeCompiled.h b/dom/xbl/nsXBLMaybeCompiled.h
index 4bd7f83960..d9d16fdfbc 100644
--- a/dom/xbl/nsXBLMaybeCompiled.h
+++ b/dom/xbl/nsXBLMaybeCompiled.h
@@ -126,15 +126,15 @@ struct IsHeapConstructibleType<nsXBLMaybeCompiled<T>>
   static const bool value = true;
 };
 
-template <class UncompiledT>
-class HeapBase<nsXBLMaybeCompiled<UncompiledT>>
+template <class UncompiledT, class Wrapper>
+class HeapBase<nsXBLMaybeCompiled<UncompiledT>, Wrapper>
 {
-  const JS::Heap<nsXBLMaybeCompiled<UncompiledT>>& wrapper() const {
-    return *static_cast<const JS::Heap<nsXBLMaybeCompiled<UncompiledT>>*>(this);
+  const Wrapper& wrapper() const {
+    return *static_cast<const Wrapper*>(this);
   }
 
-  JS::Heap<nsXBLMaybeCompiled<UncompiledT>>& wrapper() {
-    return *static_cast<JS::Heap<nsXBLMaybeCompiled<UncompiledT>>*>(this);
+  Wrapper& wrapper() {
+    return *static_cast<Wrapper*>(this);
   }
 
   const nsXBLMaybeCompiled<UncompiledT>* extract() const {
diff --git a/gfx/gl/GLContext.cpp b/gfx/gl/GLContext.cpp
index 72a7bea58b..d07b925ad5 100644
--- a/gfx/gl/GLContext.cpp
+++ b/gfx/gl/GLContext.cpp
@@ -454,6 +454,7 @@ GLContext::GLContext(CreateContextFlags flags, const SurfaceCaps& caps,
     mTopError(LOCAL_GL_NO_ERROR),
     mDebugFlags(ChooseDebugFlags(flags)),
     mSharedContext(sharedContext),
+    mSymbols{},
     mCaps(caps),
     mScreen(nullptr),
     mLockedSurface(nullptr),
@@ -519,7 +520,7 @@ GLContext::InitWithPrefix(const char* prefix, bool trygl)
 
     if (!InitWithPrefixImpl(prefix, trygl)) {
         // If initialization fails, zero the symbols to avoid hard-to-understand bugs.
-        mSymbols.Zero();
+        mSymbols = {};
         NS_WARNING("GLContext::InitWithPrefix failed!");
         return false;
     }
@@ -2205,7 +2206,7 @@ GLContext::MarkDestroyed()
     mReadTexImageHelper = nullptr;
 
     mIsDestroyed = true;
-    mSymbols.Zero();
+    mSymbols = {};
     if (MakeCurrent(true)) {
         mTexGarbageBin->GLContextTeardown();
     }
diff --git a/gfx/gl/GLContextSymbols.h b/gfx/gl/GLContextSymbols.h
index 61069e3f73..798e6cef5d 100644
--- a/gfx/gl/GLContextSymbols.h
+++ b/gfx/gl/GLContextSymbols.h
@@ -25,15 +25,9 @@
 namespace mozilla {
 namespace gl {
 
-struct GLContextSymbols
+struct GLContextSymbols final
 {
-    GLContextSymbols() {
-        Zero();
-    }
-
-    void Zero() {
-        memset(this, 0, sizeof(GLContextSymbols));
-    }
+    GLContextSymbols() = delete; // Initialize with {}.
 
     typedef void (GLAPIENTRY * PFNGLACTIVETEXTUREPROC) (GLenum texture);
     PFNGLACTIVETEXTUREPROC fActiveTexture;
diff --git a/gfx/thebes/gfxCoreTextShaper.cpp b/gfx/thebes/gfxCoreTextShaper.cpp
index 08217b82f9..254b0b63ef 100644
--- a/gfx/thebes/gfxCoreTextShaper.cpp
+++ b/gfx/thebes/gfxCoreTextShaper.cpp
@@ -310,6 +310,8 @@ gfxCoreTextShaper::SetGlyphsFromRun(gfxShapedText *aShapedText,
                                     CTRunRef       aCTRun,
                                     int32_t        aStringOffset)
 {
+    typedef gfxShapedText::CompressedGlyph CompressedGlyph;
+
     // The word has been bidi-wrapped; aStringOffset is the number
     // of chars at the beginning of the CTLine that we should skip.
     // aCTRun is a glyph run from the CoreText layout process.
@@ -392,8 +394,7 @@ gfxCoreTextShaper::SetGlyphsFromRun(gfxShapedText *aShapedText,
                                                   nullptr, nullptr, nullptr);
 
     AutoTArray<gfxShapedText::DetailedGlyph,1> detailedGlyphs;
-    gfxShapedText::CompressedGlyph *charGlyphs =
-        aShapedText->GetCharacterGlyphs() + aOffset;
+    CompressedGlyph* charGlyphs = aShapedText->GetCharacterGlyphs() + aOffset;
 
     // CoreText gives us the glyphindex-to-charindex mapping, which relates each glyph
     // to a source text character; we also need the charindex-to-glyphindex mapping to
@@ -614,10 +615,10 @@ gfxCoreTextShaper::SetGlyphsFromRun(gfxShapedText *aShapedText,
                 advance = int32_t(toNextGlyph * appUnitsPerDevUnit);
             }
 
-            gfxTextRun::CompressedGlyph textRunGlyph;
-            textRunGlyph.SetComplex(charGlyphs[baseCharIndex].IsClusterStart(),
-                                    true, detailedGlyphs.Length());
-            aShapedText->SetGlyphs(aOffset + baseCharIndex, textRunGlyph,
+            bool isClusterStart = charGlyphs[baseCharIndex].IsClusterStart();
+            aShapedText->SetGlyphs(aOffset + baseCharIndex,
+                                   CompressedGlyph::MakeComplex(isClusterStart, true,
+                                                                detailedGlyphs.Length()),
                                    detailedGlyphs.Elements());
 
             detailedGlyphs.Clear();
@@ -625,7 +626,7 @@ gfxCoreTextShaper::SetGlyphsFromRun(gfxShapedText *aShapedText,
 
         // the rest of the chars in the group are ligature continuations, no associated glyphs
         while (++baseCharIndex != endCharIndex && baseCharIndex < wordLength) {
-            gfxShapedText::CompressedGlyph &shapedTextGlyph = charGlyphs[baseCharIndex];
+            CompressedGlyph &shapedTextGlyph = charGlyphs[baseCharIndex];
             NS_ASSERTION(!shapedTextGlyph.IsSimpleGlyph(), "overwriting a simple glyph");
             shapedTextGlyph.SetComplex(inOrder && shapedTextGlyph.IsClusterStart(), false, 0);
         }
diff --git a/gfx/thebes/gfxFT2Fonts.cpp b/gfx/thebes/gfxFT2Fonts.cpp
index 1902541911..dfb94bbb69 100644
--- a/gfx/thebes/gfxFT2Fonts.cpp
+++ b/gfx/thebes/gfxFT2Fonts.cpp
@@ -62,13 +62,14 @@ void
 gfxFT2Font::AddRange(const char16_t *aText, uint32_t aOffset,
                      uint32_t aLength, gfxShapedText *aShapedText)
 {
+    typedef gfxShapedText::CompressedGlyph CompressedGlyph;
+
     const uint32_t appUnitsPerDevUnit = aShapedText->GetAppUnitsPerDevUnit();
     // we'll pass this in/figure it out dynamically, but at this point there can be only one face.
     gfxFT2LockedFace faceLock(this);
     FT_Face face = faceLock.get();
 
-    gfxShapedText::CompressedGlyph *charGlyphs =
-        aShapedText->GetCharacterGlyphs();
+    CompressedGlyph* charGlyphs = aShapedText->GetCharacterGlyphs();
 
     const gfxFT2Font::CachedGlyphData *cgd = nullptr, *cgdNext = nullptr;
 
@@ -135,8 +136,8 @@ gfxFT2Font::AddRange(const char16_t *aText, uint32_t aOffset,
         }
 
         if (advance >= 0 &&
-            gfxShapedText::CompressedGlyph::IsSimpleAdvance(advance) &&
-            gfxShapedText::CompressedGlyph::IsSimpleGlyphID(gid)) {
+            CompressedGlyph::IsSimpleAdvance(advance) &&
+            CompressedGlyph::IsSimpleGlyphID(gid)) {
             charGlyphs[aOffset].SetSimpleGlyph(advance, gid);
         } else if (gid == 0) {
             // gid = 0 only happens when the glyph is missing from the font
@@ -149,9 +150,11 @@ gfxFT2Font::AddRange(const char16_t *aText, uint32_t aOffset,
             details.mAdvance = advance;
             details.mXOffset = 0;
             details.mYOffset = 0;
-            gfxShapedText::CompressedGlyph g;
-            g.SetComplex(charGlyphs[aOffset].IsClusterStart(), true, 1);
-            aShapedText->SetGlyphs(aOffset, g, &details);
+            bool isClusterStart = charGlyphs[aOffset].IsClusterStart();
+            aShapedText->SetGlyphs(aOffset,
+                                   CompressedGlyph::MakeComplex(isClusterStart,
+                                                                true, 1),
+                                   &details);
         }
     }
 }
diff --git a/gfx/thebes/gfxFont.cpp b/gfx/thebes/gfxFont.cpp
index 9acfdeb95f..f79c5cbd72 100644
--- a/gfx/thebes/gfxFont.cpp
+++ b/gfx/thebes/gfxFont.cpp
@@ -639,10 +639,10 @@ gfxShapedText::SetupClusterBoundaries(uint32_t        aOffset,
                                       const char16_t *aString,
                                       uint32_t        aLength)
 {
-    CompressedGlyph *glyphs = GetCharacterGlyphs() + aOffset;
+    CompressedGlyph* glyphs = GetCharacterGlyphs() + aOffset;
 
-    gfxTextRun::CompressedGlyph extendCluster;
-    extendCluster.SetComplex(false, true, 0);
+    CompressedGlyph extendCluster =
+        CompressedGlyph::MakeComplex(false, true, 0);
 
     ClusterIterator iter(aString, aLength);
 
diff --git a/gfx/thebes/gfxFont.h b/gfx/thebes/gfxFont.h
index ab1677b9c5..36687585a9 100644
--- a/gfx/thebes/gfxFont.h
+++ b/gfx/thebes/gfxFont.h
@@ -245,7 +245,7 @@ struct gfxTextRange {
 
 /**
  * Font cache design:
- * 
+ *
  * The mFonts hashtable contains most fonts, indexed by (gfxFontEntry*, style).
  * It does not add a reference to the fonts it contains.
  * When a font's refcount decreases to zero, instead of deleting it we
@@ -699,21 +699,19 @@ public:
      * This class records the information associated with a character in the
      * input string. It's optimized for the case where there is one glyph
      * representing that character alone.
-     * 
+     *
      * A character can have zero or more associated glyphs. Each glyph
      * has an advance width and an x and y offset.
      * A character may be the start of a cluster.
      * A character may be the start of a ligature group.
      * A character can be "missing", indicating that the system is unable
      * to render the character.
-     * 
+     *
      * All characters in a ligature group conceptually share all the glyphs
      * associated with the characters in a group.
      */
     class CompressedGlyph {
     public:
-        CompressedGlyph() { mValue = 0; }
-
         enum {
             // Indicates that a cluster and ligature group starts at this
             // character; this character has a single glyph with a reasonable
@@ -843,25 +841,52 @@ public:
             return toggle;
         }
 
-        CompressedGlyph& SetSimpleGlyph(uint32_t aAdvanceAppUnits, uint32_t aGlyph) {
+        // Create a CompressedGlyph value representing a simple glyph with
+        // no extra flags (line-break or is_space) set.
+        static CompressedGlyph
+        MakeSimpleGlyph(uint32_t aAdvanceAppUnits, uint32_t aGlyph) {
             NS_ASSERTION(IsSimpleAdvance(aAdvanceAppUnits), "Advance overflow");
             NS_ASSERTION(IsSimpleGlyphID(aGlyph), "Glyph overflow");
+            CompressedGlyph g;
+            g.mValue = FLAG_IS_SIMPLE_GLYPH |
+                       (aAdvanceAppUnits << ADVANCE_SHIFT) |
+                       aGlyph;
+            return g;
+        }
+
+        // Assign a simple glyph value to an existing CompressedGlyph record,
+        // preserving line-break/is-space flags if present.
+        CompressedGlyph& SetSimpleGlyph(uint32_t aAdvanceAppUnits,
+                                        uint32_t aGlyph) {
             NS_ASSERTION(!CharTypeFlags(), "Char type flags lost");
             mValue = (mValue & (FLAGS_CAN_BREAK_BEFORE | FLAG_CHAR_IS_SPACE)) |
-                FLAG_IS_SIMPLE_GLYPH |
-                (aAdvanceAppUnits << ADVANCE_SHIFT) | aGlyph;
+                MakeSimpleGlyph(aAdvanceAppUnits, aGlyph).mValue;
             return *this;
         }
+
+        // Create a CompressedGlyph value representing a complex glyph record,
+        // without any line-break or char-type flags.
+        static CompressedGlyph
+        MakeComplex(bool aClusterStart, bool aLigatureStart,
+                    uint32_t aGlyphCount) {
+            CompressedGlyph g;
+            g.mValue = FLAG_NOT_MISSING |
+                       (aClusterStart ? 0 : FLAG_NOT_CLUSTER_START) |
+                       (aLigatureStart ? 0 : FLAG_NOT_LIGATURE_GROUP_START) |
+                       (aGlyphCount << GLYPH_COUNT_SHIFT);
+            return g;
+        }
+
+        // Assign a complex glyph value to an existing CompressedGlyph record,
+        // preserving line-break/char-type flags if present.
         CompressedGlyph& SetComplex(bool aClusterStart, bool aLigatureStart,
-                uint32_t aGlyphCount) {
+                                    uint32_t aGlyphCount) {
             mValue = (mValue & (FLAGS_CAN_BREAK_BEFORE | FLAG_CHAR_IS_SPACE)) |
-                FLAG_NOT_MISSING |
                 CharTypeFlags() |
-                (aClusterStart ? 0 : FLAG_NOT_CLUSTER_START) |
-                (aLigatureStart ? 0 : FLAG_NOT_LIGATURE_GROUP_START) |
-                (aGlyphCount << GLYPH_COUNT_SHIFT);
+                MakeComplex(aClusterStart, aLigatureStart, aGlyphCount).mValue;
             return *this;
         }
+
         /**
          * Missing glyphs are treated as ligature group starts; don't mess with
          * the cluster-start flag (see bugs 618870 and 619286).
@@ -914,7 +939,7 @@ public:
         /** The advance, x-offset and y-offset of the glyph, in appunits
          *  mAdvance is in the text direction (RTL or LTR)
          *  mXOffset is always from left to right
-         *  mYOffset is always from top to bottom */   
+         *  mYOffset is always from top to bottom */
         int32_t  mAdvance;
         float    mXOffset, mYOffset;
     };
@@ -1039,7 +1064,7 @@ protected:
 
     // For characters whose glyph data does not fit the "simple" glyph criteria
     // in CompressedGlyph, we use a sorted array to store the association
-    // between the source character offset and an index into an array 
+    // between the source character offset and an index into an array
     // DetailedGlyphs. The CompressedGlyph record includes a count of
     // the number of DetailedGlyph records that belong to the character,
     // starting at the given index.
@@ -1581,11 +1606,11 @@ public:
         // (offset1, length1) plus the advance width of (offset1 + length1,
         // length2) should be the advance width of (offset1, length1 + length2)
         gfxFloat mAdvanceWidth;
-        
+
         // For zero-width substrings, these must be zero!
         gfxFloat mAscent;  // always non-negative
         gfxFloat mDescent; // always non-negative
-        
+
         // Bounding box that is guaranteed to include everything drawn.
         // If a tight boundingBox was requested when these metrics were
         // generated, this will tightly wrap the glyphs, otherwise it is
@@ -1648,11 +1673,11 @@ public:
      * @param aSpacing spacing to insert before and after glyphs. The bounding box
      * need not include the spacing itself, but the spacing affects the glyph
      * positions. null if there is no spacing.
-     * 
+     *
      * Callers guarantee:
      * -- aStart and aEnd are aligned to cluster and ligature boundaries
      * -- all glyphs use this font
-     * 
+     *
      * The default implementation just uses font metrics and aTextRun's
      * advances, and assumes no characters fall outside the font box. In
      * general this is insufficient, because that assumption is not always true.
@@ -1707,7 +1732,7 @@ public:
             (mUnicodeRangeMap && !mUnicodeRangeMap->test(ch))) {
             return false;
         }
-        return mFontEntry->HasCharacter(ch); 
+        return mFontEntry->HasCharacter(ch);
     }
 
     const gfxCharacterMap* GetUnicodeRangeMap() const {
@@ -1722,7 +1747,7 @@ public:
         if (!mIsValid) {
             return 0;
         }
-        return mFontEntry->GetUVSGlyph(aCh, aVS); 
+        return mFontEntry->GetUVSGlyph(aCh, aVS);
     }
 
     template<typename T>
diff --git a/gfx/thebes/gfxGraphiteShaper.cpp b/gfx/thebes/gfxGraphiteShaper.cpp
index aeebf30f28..fe93f376f4 100644
--- a/gfx/thebes/gfxGraphiteShaper.cpp
+++ b/gfx/thebes/gfxGraphiteShaper.cpp
@@ -215,6 +215,8 @@ gfxGraphiteShaper::SetGlyphsFromSegment(DrawTarget      *aDrawTarget,
                                         const char16_t *aText,
                                         gr_segment      *aSegment)
 {
+    typedef gfxShapedText::CompressedGlyph CompressedGlyph;
+
     int32_t dev2appUnits = aShapedText->GetAppUnitsPerDevUnit();
     bool rtl = aShapedText->IsRightToLeft();
 
@@ -291,8 +293,7 @@ gfxGraphiteShaper::SetGlyphsFromSegment(DrawTarget      *aDrawTarget,
     bool roundX, roundY;
     GetRoundOffsetsToPixels(aDrawTarget, &roundX, &roundY);
 
-    gfxShapedText::CompressedGlyph *charGlyphs =
-        aShapedText->GetCharacterGlyphs() + aOffset;
+    CompressedGlyph* charGlyphs = aShapedText->GetCharacterGlyphs() + aOffset;
 
     // now put glyphs into the textrun, one cluster at a time
     for (uint32_t i = 0; i <= cIndex; ++i) {
@@ -325,8 +326,8 @@ gfxGraphiteShaper::SetGlyphsFromSegment(DrawTarget      *aDrawTarget,
         uint32_t appAdvance = roundX ? NSToIntRound(adv) * dev2appUnits :
                                        NSToIntRound(adv * dev2appUnits);
         if (c.nGlyphs == 1 &&
-            gfxShapedText::CompressedGlyph::IsSimpleGlyphID(gids[c.baseGlyph]) &&
-            gfxShapedText::CompressedGlyph::IsSimpleAdvance(appAdvance) &&
+            CompressedGlyph::IsSimpleGlyphID(gids[c.baseGlyph]) &&
+            CompressedGlyph::IsSimpleAdvance(appAdvance) &&
             charGlyphs[offs].IsClusterStart() &&
             yLocs[c.baseGlyph] == 0)
         {
@@ -352,15 +353,17 @@ gfxGraphiteShaper::SetGlyphsFromSegment(DrawTarget      *aDrawTarget,
                     d->mAdvance = 0;
                 }
             }
-            gfxShapedText::CompressedGlyph g;
-            g.SetComplex(charGlyphs[offs].IsClusterStart(),
-                         true, details.Length());
-            aShapedText->SetGlyphs(aOffset + offs, g, details.Elements());
+            bool isClusterStart = charGlyphs[offs].IsClusterStart();
+            aShapedText->SetGlyphs(aOffset + offs,
+                                   CompressedGlyph::MakeComplex(isClusterStart,
+                                                                true,
+                                                                details.Length()),
+                                   details.Elements());
         }
 
         for (uint32_t j = c.baseChar + 1; j < c.baseChar + c.nChars; ++j) {
             NS_ASSERTION(j < aLength, "unexpected offset");
-            gfxShapedText::CompressedGlyph &g = charGlyphs[j];
+            CompressedGlyph &g = charGlyphs[j];
             NS_ASSERTION(!g.IsSimpleGlyph(), "overwriting a simple glyph");
             g.SetComplex(g.IsClusterStart(), false, 0);
         }
diff --git a/gfx/thebes/gfxHarfBuzzShaper.cpp b/gfx/thebes/gfxHarfBuzzShaper.cpp
index 4a563a95f9..7f05f9011f 100644
--- a/gfx/thebes/gfxHarfBuzzShaper.cpp
+++ b/gfx/thebes/gfxHarfBuzzShaper.cpp
@@ -817,7 +817,7 @@ GetKernValueVersion1Fmt3(const void* aSubtable,
         hdr->leftClassCount * hdr->rightClassCount > aSubtableLen) {
         return 0;
     }
-        
+
     if (aFirstGlyph >= glyphCount || aSecondGlyph >= glyphCount) {
         // glyphs are out of range for the class tables
         return 0;
@@ -1503,6 +1503,8 @@ gfxHarfBuzzShaper::SetGlyphsFromRun(DrawTarget     *aDrawTarget,
                                     hb_buffer_t    *aBuffer,
                                     bool            aVertical)
 {
+    typedef gfxShapedText::CompressedGlyph CompressedGlyph;
+
     uint32_t numGlyphs;
     const hb_glyph_info_t *ginfo = hb_buffer_get_glyph_infos(aBuffer, &numGlyphs);
     if (numGlyphs == 0) {
@@ -1541,8 +1543,7 @@ gfxHarfBuzzShaper::SetGlyphsFromRun(DrawTarget     *aDrawTarget,
     }
 
     int32_t appUnitsPerDevUnit = aShapedText->GetAppUnitsPerDevUnit();
-    gfxShapedText::CompressedGlyph *charGlyphs =
-        aShapedText->GetCharacterGlyphs() + aOffset;
+    CompressedGlyph* charGlyphs = aShapedText->GetCharacterGlyphs() + aOffset;
 
     // factor to convert 16.16 fixed-point pixels to app units
     // (only used if not rounding)
@@ -1688,8 +1689,8 @@ gfxHarfBuzzShaper::SetGlyphsFromRun(DrawTarget     *aDrawTarget,
         }
         // Check if it's a simple one-to-one mapping
         if (glyphsInClump == 1 &&
-            gfxTextRun::CompressedGlyph::IsSimpleGlyphID(ginfo[glyphStart].codepoint) &&
-            gfxTextRun::CompressedGlyph::IsSimpleAdvance(advance) &&
+            CompressedGlyph::IsSimpleGlyphID(ginfo[glyphStart].codepoint) &&
+            CompressedGlyph::IsSimpleAdvance(advance) &&
             charGlyphs[baseCharIndex].IsClusterStart() &&
             iOffset == 0 && b_offset == 0 &&
             b_advance == 0 && bPos == 0)
@@ -1760,11 +1761,12 @@ gfxHarfBuzzShaper::SetGlyphsFromRun(DrawTarget     *aDrawTarget,
                 }
             }
 
-            gfxShapedText::CompressedGlyph g;
-            g.SetComplex(charGlyphs[baseCharIndex].IsClusterStart(),
-                         true, detailedGlyphs.Length());
+            bool isClusterStart = charGlyphs[baseCharIndex].IsClusterStart();
             aShapedText->SetGlyphs(aOffset + baseCharIndex,
-                                   g, detailedGlyphs.Elements());
+                                   CompressedGlyph::MakeComplex(isClusterStart,
+                                                                true,
+                                                                detailedGlyphs.Length()),
+                                   detailedGlyphs.Elements());
 
             detailedGlyphs.Clear();
         }
@@ -1773,7 +1775,7 @@ gfxHarfBuzzShaper::SetGlyphsFromRun(DrawTarget     *aDrawTarget,
         // no associated glyphs
         while (++baseCharIndex != endCharIndex &&
                baseCharIndex < int32_t(wordLength)) {
-            gfxShapedText::CompressedGlyph &g = charGlyphs[baseCharIndex];
+            CompressedGlyph &g = charGlyphs[baseCharIndex];
             NS_ASSERTION(!g.IsSimpleGlyph(), "overwriting a simple glyph");
             g.SetComplex(g.IsClusterStart(), false, 0);
         }
diff --git a/gfx/thebes/gfxTextRun.cpp b/gfx/thebes/gfxTextRun.cpp
index db9fc346b4..fd97615366 100644
--- a/gfx/thebes/gfxTextRun.cpp
+++ b/gfx/thebes/gfxTextRun.cpp
@@ -244,7 +244,7 @@ gfxTextRun::ComputeLigatureData(Range aPartRange,
     NS_ASSERTION(aPartRange.start < aPartRange.end,
                  "Computing ligature data for empty range");
     NS_ASSERTION(aPartRange.end <= GetLength(), "Character length overflow");
-  
+
     LigatureData result;
     const CompressedGlyph *charGlyphs = mCharacterGlyphs;
 
@@ -392,7 +392,7 @@ gfxTextRun::ShrinkToLigatureBoundaries(Range* aRange) const
 {
     if (aRange->start >= aRange->end)
         return;
-  
+
     const CompressedGlyph *charGlyphs = mCharacterGlyphs;
 
     while (aRange->start < aRange->end &&
@@ -440,7 +440,7 @@ ClipPartialLigature(const gfxTextRun* aTextRun,
         } else {
             *aEnd = std::min(*aEnd, endEdge);
         }
-    }    
+    }
 }
 
 void
@@ -789,7 +789,7 @@ gfxTextRun::AccumulatePartialLigatureMetrics(gfxFont *aFont, Range aRange,
     // ligature. Shift it left.
     metrics.mBoundingBox.x -=
         IsRightToLeft() ? metrics.mAdvanceWidth - (data.mPartAdvance + data.mPartWidth)
-            : data.mPartAdvance;    
+            : data.mPartAdvance;
     metrics.mAdvanceWidth = data.mPartWidth;
 
     aMetrics->CombineWith(metrics, IsRightToLeft());
@@ -905,7 +905,7 @@ gfxTextRun::BreakAndMeasureText(uint32_t aStart, uint32_t aMaxLength,
         }
 
         // There can't be a word-wrap break opportunity at the beginning of the
-        // line: if the width is too small for even one character to fit, it 
+        // line: if the width is too small for even one character to fit, it
         // could be the first and last break opportunity on the line, and that
         // would trigger an infinite loop.
         if (aSuppressBreak != eSuppressAllBreaks &&
@@ -923,7 +923,7 @@ gfxTextRun::BreakAndMeasureText(uint32_t aStart, uint32_t aMaxLength,
                 if (atHyphenationBreak) {
                     hyphenatedAdvance += aProvider->GetHyphenWidth();
                 }
-            
+
                 if (lastBreak < 0 || width + hyphenatedAdvance - trimmableAdvance <= aWidth) {
                     // We can break here.
                     lastBreak = i;
@@ -943,7 +943,7 @@ gfxTextRun::BreakAndMeasureText(uint32_t aStart, uint32_t aMaxLength,
                 }
             }
         }
-        
+
         gfxFloat charAdvance;
         if (i >= ligatureRange.start && i < ligatureRange.end) {
             charAdvance = GetAdvanceForGlyphs(Range(i, i + 1));
@@ -956,7 +956,7 @@ gfxTextRun::BreakAndMeasureText(uint32_t aStart, uint32_t aMaxLength,
             charAdvance =
                 ComputePartialLigatureWidth(Range(i, i + 1), aProvider);
         }
-        
+
         advance += charAdvance;
         if (aTrimWhitespace || aWhitespaceCanHang) {
             if (mCharacterGlyphs[i].CharIsSpace()) {
@@ -1145,7 +1145,7 @@ gfxTextRun::AddGlyphRun(gfxFont *aFont, uint8_t aMatchType,
                  "mixed orientation should have been resolved");
     if (!aFont) {
         return NS_OK;
-    }    
+    }
     uint32_t numGlyphRuns = mGlyphRuns.Length();
     if (!aForceNewRun && numGlyphRuns > 0) {
         GlyphRun *lastGlyphRun = &mGlyphRuns[numGlyphRuns - 1];
@@ -1405,7 +1405,7 @@ gfxTextRun::SetSpaceGlyph(gfxFont* aFont, DrawTarget* aDrawTarget,
         (GetFlags() & gfxTextRunFactory::TEXT_ORIENT_VERTICAL_UPRIGHT) != 0;
     gfxShapedWord* sw = aFont->GetShapedWord(aDrawTarget,
                                              &space, 1,
-                                             gfxShapedWord::HashMix(0, ' '), 
+                                             gfxShapedWord::HashMix(0, ' '),
                                              Script::LATIN,
                                              vertical,
                                              mAppUnitsPerDevUnit,
@@ -1439,8 +1439,8 @@ gfxTextRun::SetSpaceGlyphIfSimple(gfxFont* aFont, uint32_t aCharIndex,
 
     AddGlyphRun(aFont, gfxTextRange::kFontGroup, aCharIndex, false,
                 aOrientation);
-    CompressedGlyph g;
-    g.SetSimpleGlyph(spaceWidthAppUnits, spaceGlyph);
+    CompressedGlyph g =
+        CompressedGlyph::MakeSimpleGlyph(spaceWidthAppUnits, spaceGlyph);
     if (aSpaceChar == ' ') {
         g.SetIsSpace();
     }
@@ -1471,7 +1471,7 @@ gfxTextRun::FetchGlyphExtents(DrawTarget* aRefDrawTarget)
         bool fontIsSetup = false;
         uint32_t j;
         gfxGlyphExtents *extents = font->GetOrCreateGlyphExtents(mAppUnitsPerDevUnit);
-  
+
         for (j = start; j < end; ++j) {
             const gfxTextRun::CompressedGlyph *glyphData = &charGlyphs[j];
             if (glyphData->IsSimpleGlyph()) {
@@ -1943,13 +1943,13 @@ gfxFontGroup::Copy(const gfxFontStyle *aStyle)
     return fg;
 }
 
-bool 
+bool
 gfxFontGroup::IsInvalidChar(uint8_t ch)
 {
     return ((ch & 0x7f) < 0x20 || ch == 0x7f);
 }
 
-bool 
+bool
 gfxFontGroup::IsInvalidChar(char16_t ch)
 {
     // All printable 7-bit ASCII values are OK
@@ -2514,8 +2514,8 @@ gfxFontGroup::InitScriptRun(DrawTarget* aDrawTarget,
                             detailedGlyph.mGlyphID = mainFont->GetSpaceGlyph();
                             detailedGlyph.mAdvance = advance;
                             detailedGlyph.mXOffset = detailedGlyph.mYOffset = 0;
-                            gfxShapedText::CompressedGlyph g;
-                            g.SetComplex(true, true, 1);
+                            CompressedGlyph g =
+                                CompressedGlyph::MakeComplex(true, true, 1);
                             aTextRun->SetGlyphs(aOffset + index,
                                                 g, &detailedGlyph);
                         }
@@ -3128,7 +3128,7 @@ gfxFontGroup::WhichPrefFontSupportsChar(uint32_t aCh, uint32_t aNextCh)
         uint32_t unicodeRange = FindCharUnicodeRange(aCh);
         charLang = pfl->GetFontPrefLangFor(unicodeRange);
     }
- 
+
     // if the last pref font was the first family in the pref list, no need to recheck through a list of families
     if (mLastPrefFont && charLang == mLastPrefLang &&
         mLastPrefFirstFont && mLastPrefFont->HasCharacter(aCh)) {
@@ -3190,7 +3190,7 @@ already_AddRefed<gfxFont>
 gfxFontGroup::WhichSystemFontSupportsChar(uint32_t aCh, uint32_t aNextCh,
                                           Script aRunScript)
 {
-    gfxFontEntry *fe = 
+    gfxFontEntry *fe =
         gfxPlatformFontList::PlatformFontList()->
             SystemFindFontForChar(aCh, aNextCh, aRunScript, &mStyle);
     if (fe) {
diff --git a/gfx/thebes/gfxTextRun.h b/gfx/thebes/gfxTextRun.h
index 7217eca747..d61992527b 100644
--- a/gfx/thebes/gfxTextRun.h
+++ b/gfx/thebes/gfxTextRun.h
@@ -70,7 +70,7 @@ struct gfxTextRunDrawCallbacks {
  * of text. It stores runs of positioned glyph data, each run having a single
  * gfxFont. The glyphs are associated with a string of source text, and the
  * gfxTextRun APIs take parameters that are offsets into that source text.
- * 
+ *
  * gfxTextRuns are mostly immutable. The only things that can change are
  * inter-cluster spacing and line break placement. Spacing is always obtained
  * lazily by methods that need it, it is not cached. Line breaks are stored
@@ -78,7 +78,7 @@ struct gfxTextRunDrawCallbacks {
  * not actually do anything to explicitly account for line breaks). Initially
  * there are no line breaks. The textrun can record line breaks before or after
  * any given cluster. (Line breaks specified inside clusters are ignored.)
- * 
+ *
  * It is important that zero-length substrings are handled correctly. This will
  * be on the test!
  */
@@ -163,11 +163,11 @@ public:
      * Set the potential linebreaks for a substring of the textrun. These are
      * the "allow break before" points. Initially, there are no potential
      * linebreaks.
-     * 
+     *
      * This can change glyphs and/or geometry! Some textruns' shapes
      * depend on potential line breaks (e.g., title-case-converting textruns).
      * This function is virtual so that those textruns can reshape themselves.
-     * 
+     *
      * @return true if this changed the linebreaks, false if the new line
      * breaks are the same as the old
      */
@@ -179,7 +179,7 @@ public:
      * potential line break points and computation of spacing. We pass the data
      * this way to allow lazy data acquisition; for example BreakAndMeasureText
      * will want to only ask for properties of text it's actually looking at.
-     * 
+     *
      * NOTE that requested spacing may not actually be applied, if the textrun
      * is unable to apply it in some context. Exception: spacing around a
      * whitespace character MUST always be applied.
@@ -238,7 +238,7 @@ public:
      * Draws a substring. Uses only GetSpacing from aBreakProvider.
      * The provided point is the baseline origin on the left of the string
      * for LTR, on the right of the string for RTL.
-     * 
+     *
      * Drawing should respect advance widths in the sense that for LTR runs,
      *   Draw(Range(start, middle), pt, ...) followed by
      *   Draw(Range(middle, end), gfxPoint(pt.x + advance, pt.y), ...)
@@ -250,7 +250,7 @@ public:
      *   Draw(Range(start, middle), gfxPoint(pt.x + advance, pt.y), ...)
      * should have the same effect as
      *   Draw(Range(start, end), pt, ...)
-     * 
+     *
      * Glyphs should be drawn in logical content order, which can be significant
      * if they overlap (perhaps due to negative spacing).
      */
@@ -307,14 +307,14 @@ public:
      * Clear all stored line breaks for the given range (both before and after),
      * and then set the line-break state before aRange.start to aBreakBefore and
      * after the last cluster to aBreakAfter.
-     * 
+     *
      * We require that before and after line breaks be consistent. For clusters
      * i and i+1, we require that if there is a break after cluster i, a break
      * will be specified before cluster i+1. This may be temporarily violated
      * (e.g. after reflowing line L and before reflowing line L+1); to handle
      * these temporary violations, we say that there is a break betwen i and i+1
      * if a break is specified after i OR a break is specified before i+1.
-     * 
+     *
      * This can change textrun geometry! The existence of a linebreak can affect
      * the advance width of the cluster before the break (when kerning) or the
      * geometry of one cluster before the break or any number of clusters
@@ -322,11 +322,11 @@ public:
      * arbitrary; if some scripts require breaking it, then we need to
      * alter nsTextFrame::TrimTrailingWhitespace, perhaps drastically becase
      * it could affect the layout of frames before it...)
-     * 
+     *
      * We return true if glyphs or geometry changed, false otherwise. This
      * function is virtual so that gfxTextRun subclasses can reshape
      * properly.
-     * 
+     *
      * @param aAdvanceWidthDelta if non-null, returns the change in advance
      * width of the given range.
      */
@@ -393,7 +393,7 @@ public:
      * @param aBreakPriority in/out the priority of the break opportunity
      * saved in the line. If we are prioritizing break opportunities, we will
      * not set a break with a lower priority. @see gfxBreakPriority.
-     * 
+     *
      * Note that negative advance widths are possible especially if negative
      * spacing is provided.
      */
@@ -596,11 +596,11 @@ public:
         // when the part is at the start of the ligature, and after-spacing
         // when the part is as the end of the ligature
         gfxFloat mPartWidth;
-        
+
         bool mClipBeforePart;
         bool mClipAfterPart;
     };
-    
+
     // return storage used by this run, for memory reporter;
     // nsTransformedTextRun needs to override this as it holds additional data
     virtual size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf)
@@ -681,7 +681,7 @@ protected:
     CompressedGlyph *mCharacterGlyphs;
 
 private:
-    // **** general helpers **** 
+    // **** general helpers ****
 
     // Get the total advance for a range of glyphs.
     int32_t GetAdvanceForGlyphs(Range aRange) const;
@@ -765,6 +765,7 @@ private:
 class gfxFontGroup : public gfxTextRunFactory {
 public:
     typedef mozilla::unicode::Script Script;
+    typedef gfxShapedText::CompressedGlyph CompressedGlyph;
 
     static void Shutdown(); // platform must call this to release the languageAtomService
 
diff --git a/image/imgFrame.cpp b/image/imgFrame.cpp
index 6fd1a69b61..88cef68bf9 100644
--- a/image/imgFrame.cpp
+++ b/image/imgFrame.cpp
@@ -123,7 +123,7 @@ AllowedImageSize(int32_t aWidth, int32_t aHeight)
     return false;
   }
 
-  // check to make sure we don't overflow a 32-bit
+  // check to make sure we don't overflow 32-bit size for RGBA
   CheckedInt32 requiredBytes = CheckedInt32(aWidth) * CheckedInt32(aHeight) * 4;
   if (MOZ_UNLIKELY(!requiredBytes.isValid())) {
     NS_WARNING("width or height too large");
diff --git a/js/ipc/JavaScriptShared.cpp b/js/ipc/JavaScriptShared.cpp
index 6ec339e493..6dfb00bc5e 100644
--- a/js/ipc/JavaScriptShared.cpp
+++ b/js/ipc/JavaScriptShared.cpp
@@ -100,7 +100,7 @@ IdToObjectMap::has(const ObjectId& id, const JSObject* obj) const
     auto p = table_.lookup(id);
     if (!p)
         return false;
-    return p->value().unbarrieredGet() == obj;
+    return p->value() == obj;
 }
 #endif
 
diff --git a/js/public/Class.h b/js/public/Class.h
index 6f1960a308..1dd03a1821 100644
--- a/js/public/Class.h
+++ b/js/public/Class.h
@@ -271,8 +271,119 @@ class ObjectOpResult
     }
 };
 
+class PropertyResult
+{
+    union {
+        js::Shape* shape_;
+        uintptr_t bits_;
+    };
+
+    static const uintptr_t NotFound = 0;
+    static const uintptr_t NonNativeProperty = 1;
+    static const uintptr_t DenseOrTypedArrayElement = 1;
+
+  public:
+    PropertyResult() : bits_(NotFound) {}
+
+    explicit PropertyResult(js::Shape* propertyShape)
+      : shape_(propertyShape)
+    {
+        MOZ_ASSERT(!isFound() || isNativeProperty());
+    }
+
+    explicit operator bool() const {
+        return isFound();
+    }
+
+    bool isFound() const {
+        return bits_ != NotFound;
+    }
+
+    bool isNonNativeProperty() const {
+        return bits_ == NonNativeProperty;
+    }
+
+    bool isDenseOrTypedArrayElement() const {
+        return bits_ == DenseOrTypedArrayElement;
+    }
+
+    bool isNativeProperty() const {
+        return isFound() && !isNonNativeProperty();
+    }
+
+    js::Shape* maybeShape() const {
+        MOZ_ASSERT(!isNonNativeProperty());
+        return isFound() ? shape_ : nullptr;
+    }
+
+    js::Shape* shape() const {
+        MOZ_ASSERT(isNativeProperty());
+        return shape_;
+    }
+
+    void setNotFound() {
+        bits_ = NotFound;
+    }
+
+    void setNativeProperty(js::Shape* propertyShape) {
+        shape_ = propertyShape;
+        MOZ_ASSERT(isNativeProperty());
+    }
+
+    void setNonNativeProperty() {
+        bits_ = NonNativeProperty;
+    }
+
+    void setDenseOrTypedArrayElement() {
+        bits_ = DenseOrTypedArrayElement;
+    }
+
+    void trace(JSTracer* trc);
+};
+
 } // namespace JS
 
+namespace js {
+
+template <class Wrapper>
+class WrappedPtrOperations<JS::PropertyResult, Wrapper>
+{
+    const JS::PropertyResult& value() const { return static_cast<const Wrapper*>(this)->get(); }
+
+  public:
+    bool isFound() const { return value().isFound(); }
+    explicit operator bool() const { return bool(value()); }
+    js::Shape* maybeShape() const { return value().maybeShape(); }
+    js::Shape* shape() const { return value().shape(); }
+    bool isNativeProperty() const { return value().isNativeProperty(); }
+    bool isNonNativeProperty() const { return value().isNonNativeProperty(); }
+    bool isDenseOrTypedArrayElement() const { return value().isDenseOrTypedArrayElement(); }
+    js::Shape* asTaggedShape() const { return value().asTaggedShape(); }
+};
+
+template <class Wrapper>
+class MutableWrappedPtrOperations<JS::PropertyResult, Wrapper>
+  : public WrappedPtrOperations<JS::PropertyResult, Wrapper>
+{
+    JS::PropertyResult& value() { return static_cast<Wrapper*>(this)->get(); }
+
+  public:
+    void setNotFound() {
+        value().setNotFound();
+    }
+    void setNativeProperty(js::Shape* shape) {
+        value().setNativeProperty(shape);
+    }
+    void setNonNativeProperty() {
+        value().setNonNativeProperty();
+    }
+    void setDenseOrTypedArrayElement() {
+        value().setDenseOrTypedArrayElement();
+    }
+};
+
+} // namespace js
+
 // JSClass operation signatures.
 
 /**
@@ -428,7 +539,7 @@ namespace js {
 
 typedef bool
 (* LookupPropertyOp)(JSContext* cx, JS::HandleObject obj, JS::HandleId id,
-                     JS::MutableHandleObject objp, JS::MutableHandle<Shape*> propp);
+                     JS::MutableHandleObject objp, JS::MutableHandle<JS::PropertyResult> propp);
 typedef bool
 (* DefinePropertyOp)(JSContext* cx, JS::HandleObject obj, JS::HandleId id,
                      JS::Handle<JS::PropertyDescriptor> desc,
diff --git a/js/public/GCHashTable.h b/js/public/GCHashTable.h
index 4de1c39a81..3e647ed100 100644
--- a/js/public/GCHashTable.h
+++ b/js/public/GCHashTable.h
@@ -133,13 +133,13 @@ class GCRekeyableHashMap : public JS::GCHashMap<Key, Value, HashPolicy, AllocPol
     }
 };
 
-template <typename Outer, typename... Args>
-class GCHashMapOperations
+template <typename Wrapper, typename... Args>
+class WrappedPtrOperations<JS::GCHashMap<Args...>, Wrapper>
 {
     using Map = JS::GCHashMap<Args...>;
     using Lookup = typename Map::Lookup;
 
-    const Map& map() const { return static_cast<const Outer*>(this)->get(); }
+    const Map& map() const { return static_cast<const Wrapper*>(this)->get(); }
 
   public:
     using AddPtr = typename Map::AddPtr;
@@ -162,18 +162,18 @@ class GCHashMapOperations
     }
 };
 
-template <typename Outer, typename... Args>
-class MutableGCHashMapOperations
-  : public GCHashMapOperations<Outer, Args...>
+template <typename Wrapper, typename... Args>
+class MutableWrappedPtrOperations<JS::GCHashMap<Args...>, Wrapper>
+  : public WrappedPtrOperations<JS::GCHashMap<Args...>, Wrapper>
 {
     using Map = JS::GCHashMap<Args...>;
     using Lookup = typename Map::Lookup;
 
-    Map& map() { return static_cast<Outer*>(this)->get(); }
+    Map& map() { return static_cast<Wrapper*>(this)->get(); }
 
   public:
     using AddPtr = typename Map::AddPtr;
-    struct Enum : public Map::Enum { explicit Enum(Outer& o) : Map::Enum(o.map()) {} };
+    struct Enum : public Map::Enum { explicit Enum(Wrapper& o) : Map::Enum(o.map()) {} };
     using Ptr = typename Map::Ptr;
     using Range = typename Map::Range;
 
@@ -210,26 +210,6 @@ class MutableGCHashMapOperations
     }
 };
 
-template <typename A, typename B, typename C, typename D, typename E>
-class RootedBase<JS::GCHashMap<A,B,C,D,E>>
-  : public MutableGCHashMapOperations<JS::Rooted<JS::GCHashMap<A,B,C,D,E>>, A,B,C,D,E>
-{};
-
-template <typename A, typename B, typename C, typename D, typename E>
-class MutableHandleBase<JS::GCHashMap<A,B,C,D,E>>
-  : public MutableGCHashMapOperations<JS::MutableHandle<JS::GCHashMap<A,B,C,D,E>>, A,B,C,D,E>
-{};
-
-template <typename A, typename B, typename C, typename D, typename E>
-class HandleBase<JS::GCHashMap<A,B,C,D,E>>
-  : public GCHashMapOperations<JS::Handle<JS::GCHashMap<A,B,C,D,E>>, A,B,C,D,E>
-{};
-
-template <typename A, typename B, typename C, typename D, typename E>
-class WeakCacheBase<JS::GCHashMap<A,B,C,D,E>>
-  : public MutableGCHashMapOperations<JS::WeakCache<JS::GCHashMap<A,B,C,D,E>>, A,B,C,D,E>
-{};
-
 } // namespace js
 
 namespace JS {
@@ -291,13 +271,13 @@ class GCHashSet : public js::HashSet<T, HashPolicy, AllocPolicy>
 
 namespace js {
 
-template <typename Outer, typename... Args>
-class GCHashSetOperations
+template <typename Wrapper, typename... Args>
+class WrappedPtrOperations<JS::GCHashSet<Args...>, Wrapper>
 {
     using Set = JS::GCHashSet<Args...>;
     using Lookup = typename Set::Lookup;
 
-    const Set& set() const { return static_cast<const Outer*>(this)->get(); }
+    const Set& set() const { return static_cast<const Wrapper*>(this)->get(); }
 
   public:
     using AddPtr = typename Set::AddPtr;
@@ -321,19 +301,19 @@ class GCHashSetOperations
     }
 };
 
-template <typename Outer, typename... Args>
-class MutableGCHashSetOperations
-  : public GCHashSetOperations<Outer, Args...>
+template <typename Wrapper, typename... Args>
+class MutableWrappedPtrOperations<JS::GCHashSet<Args...>, Wrapper>
+  : public WrappedPtrOperations<JS::GCHashSet<Args...>, Wrapper>
 {
     using Set = JS::GCHashSet<Args...>;
     using Lookup = typename Set::Lookup;
 
-    Set& set() { return static_cast<Outer*>(this)->get(); }
+    Set& set() { return static_cast<Wrapper*>(this)->get(); }
 
   public:
     using AddPtr = typename Set::AddPtr;
     using Entry = typename Set::Entry;
-    struct Enum : public Set::Enum { explicit Enum(Outer& o) : Set::Enum(o.set()) {} };
+    struct Enum : public Set::Enum { explicit Enum(Wrapper& o) : Set::Enum(o.set()) {} };
     using Ptr = typename Set::Ptr;
     using Range = typename Set::Range;
 
@@ -369,30 +349,6 @@ class MutableGCHashSetOperations
     }
 };
 
-template <typename T, typename HP, typename AP>
-class RootedBase<JS::GCHashSet<T, HP, AP>>
-  : public MutableGCHashSetOperations<JS::Rooted<JS::GCHashSet<T, HP, AP>>, T, HP, AP>
-{
-};
-
-template <typename T, typename HP, typename AP>
-class MutableHandleBase<JS::GCHashSet<T, HP, AP>>
-  : public MutableGCHashSetOperations<JS::MutableHandle<JS::GCHashSet<T, HP, AP>>, T, HP, AP>
-{
-};
-
-template <typename T, typename HP, typename AP>
-class HandleBase<JS::GCHashSet<T, HP, AP>>
-  : public GCHashSetOperations<JS::Handle<JS::GCHashSet<T, HP, AP>>, T, HP, AP>
-{
-};
-
-template <typename T, typename HP, typename AP>
-class WeakCacheBase<JS::GCHashSet<T, HP, AP>>
-  : public MutableGCHashSetOperations<JS::WeakCache<JS::GCHashSet<T, HP, AP>>, T, HP, AP>
-{
-};
-
 } /* namespace js */
 
 #endif /* GCHashTable_h */
diff --git a/js/public/GCVariant.h b/js/public/GCVariant.h
index 43f2957fee..3ec40df5ca 100644
--- a/js/public/GCVariant.h
+++ b/js/public/GCVariant.h
@@ -123,13 +123,13 @@ struct GCPolicy<mozilla::Variant<Ts...>>
 
 namespace js {
 
-template <typename Outer, typename... Ts>
-class GCVariantOperations
+template <typename Wrapper, typename... Ts>
+class WrappedPtrOperations<mozilla::Variant<Ts...>, Wrapper>
 {
     using Impl = JS::detail::GCVariantImplementation<Ts...>;
     using Variant = mozilla::Variant<Ts...>;
 
-    const Variant& variant() const { return static_cast<const Outer*>(this)->get(); }
+    const Variant& variant() const { return static_cast<const Wrapper*>(this)->get(); }
 
   public:
     template <typename T>
@@ -149,15 +149,15 @@ class GCVariantOperations
     }
 };
 
-template <typename Outer, typename... Ts>
-class MutableGCVariantOperations
-  : public GCVariantOperations<Outer, Ts...>
+template <typename Wrapper, typename... Ts>
+class MutableWrappedPtrOperations<mozilla::Variant<Ts...>, Wrapper>
+  : public WrappedPtrOperations<mozilla::Variant<Ts...>, Wrapper>
 {
     using Impl = JS::detail::GCVariantImplementation<Ts...>;
     using Variant = mozilla::Variant<Ts...>;
 
-    const Variant& variant() const { return static_cast<const Outer*>(this)->get(); }
-    Variant& variant() { return static_cast<Outer*>(this)->get(); }
+    const Variant& variant() const { return static_cast<const Wrapper*>(this)->get(); }
+    Variant& variant() { return static_cast<Wrapper*>(this)->get(); }
 
   public:
     template <typename T>
@@ -172,26 +172,6 @@ class MutableGCVariantOperations
     }
 };
 
-template <typename... Ts>
-class RootedBase<mozilla::Variant<Ts...>>
-  : public MutableGCVariantOperations<JS::Rooted<mozilla::Variant<Ts...>>, Ts...>
-{ };
-
-template <typename... Ts>
-class MutableHandleBase<mozilla::Variant<Ts...>>
-  : public MutableGCVariantOperations<JS::MutableHandle<mozilla::Variant<Ts...>>, Ts...>
-{ };
-
-template <typename... Ts>
-class HandleBase<mozilla::Variant<Ts...>>
-  : public GCVariantOperations<JS::Handle<mozilla::Variant<Ts...>>, Ts...>
-{ };
-
-template <typename... Ts>
-class PersistentRootedBase<mozilla::Variant<Ts...>>
-  : public MutableGCVariantOperations<JS::PersistentRooted<mozilla::Variant<Ts...>>, Ts...>
-{ };
-
 } // namespace js
 
 #endif // js_GCVariant_h
diff --git a/js/public/GCVector.h b/js/public/GCVector.h
index 1c99252617..4acf0d1fc5 100644
--- a/js/public/GCVector.h
+++ b/js/public/GCVector.h
@@ -134,11 +134,11 @@ class GCVector
 
 namespace js {
 
-template <typename Outer, typename T, size_t Capacity, typename AllocPolicy>
-class GCVectorOperations
+template <typename Wrapper, typename T, size_t Capacity, typename AllocPolicy>
+class WrappedPtrOperations<JS::GCVector<T, Capacity, AllocPolicy>, Wrapper>
 {
     using Vec = JS::GCVector<T, Capacity, AllocPolicy>;
-    const Vec& vec() const { return static_cast<const Outer*>(this)->get(); }
+    const Vec& vec() const { return static_cast<const Wrapper*>(this)->get(); }
 
   public:
     const AllocPolicy& allocPolicy() const { return vec().allocPolicy(); }
@@ -154,13 +154,13 @@ class GCVectorOperations
     }
 };
 
-template <typename Outer, typename T, size_t Capacity, typename AllocPolicy>
-class MutableGCVectorOperations
-  : public GCVectorOperations<Outer, T, Capacity, AllocPolicy>
+template <typename Wrapper, typename T, size_t Capacity, typename AllocPolicy>
+class MutableWrappedPtrOperations<JS::GCVector<T, Capacity, AllocPolicy>, Wrapper>
+  : public WrappedPtrOperations<JS::GCVector<T, Capacity, AllocPolicy>, Wrapper>
 {
     using Vec = JS::GCVector<T, Capacity, AllocPolicy>;
-    const Vec& vec() const { return static_cast<const Outer*>(this)->get(); }
-    Vec& vec() { return static_cast<Outer*>(this)->get(); }
+    const Vec& vec() const { return static_cast<const Wrapper*>(this)->get(); }
+    Vec& vec() { return static_cast<Wrapper*>(this)->get(); }
 
   public:
     const AllocPolicy& allocPolicy() const { return vec().allocPolicy(); }
@@ -223,26 +223,6 @@ class MutableGCVectorOperations
     void erase(T* aBegin, T* aEnd) { vec().erase(aBegin, aEnd); }
 };
 
-template <typename T, size_t N, typename AP>
-class RootedBase<JS::GCVector<T,N,AP>>
-  : public MutableGCVectorOperations<JS::Rooted<JS::GCVector<T,N,AP>>, T,N,AP>
-{};
-
-template <typename T, size_t N, typename AP>
-class MutableHandleBase<JS::GCVector<T,N,AP>>
-  : public MutableGCVectorOperations<JS::MutableHandle<JS::GCVector<T,N,AP>>, T,N,AP>
-{};
-
-template <typename T, size_t N, typename AP>
-class HandleBase<JS::GCVector<T,N,AP>>
-  : public GCVectorOperations<JS::Handle<JS::GCVector<T,N,AP>>, T,N,AP>
-{};
-
-template <typename T, size_t N, typename AP>
-class PersistentRootedBase<JS::GCVector<T,N,AP>>
-  : public MutableGCVectorOperations<JS::PersistentRooted<JS::GCVector<T,N,AP>>, T,N,AP>
-{};
-
 } // namespace js
 
 #endif // js_GCVector_h
diff --git a/js/public/RootingAPI.h b/js/public/RootingAPI.h
index 5f0740d53a..aec25b0ffe 100644
--- a/js/public/RootingAPI.h
+++ b/js/public/RootingAPI.h
@@ -112,17 +112,23 @@ template <typename T>
 struct BarrierMethods {
 };
 
-template <typename T>
-class RootedBase {};
+template <typename Element, typename Wrapper>
+class WrappedPtrOperations {};
 
-template <typename T>
-class HandleBase {};
+template <typename Element, typename Wrapper>
+class MutableWrappedPtrOperations : public WrappedPtrOperations<Element, Wrapper> {};
 
-template <typename T>
-class MutableHandleBase {};
+template <typename T, typename Wrapper>
+class RootedBase : public MutableWrappedPtrOperations<T, Wrapper> {};
 
-template <typename T>
-class HeapBase {};
+template <typename T, typename Wrapper>
+class HandleBase : public WrappedPtrOperations<T, Wrapper> {};
+
+template <typename T, typename Wrapper>
+class MutableHandleBase : public MutableWrappedPtrOperations<T, Wrapper> {};
+
+template <typename T, typename Wrapper>
+class HeapBase : public MutableWrappedPtrOperations<T, Wrapper> {};
 
 // Cannot use FOR_EACH_HEAP_ABLE_GC_POINTER_TYPE, as this would import too many macros into scope
 template <typename T> struct IsHeapConstructibleType    { static constexpr bool value = false; };
@@ -132,8 +138,8 @@ FOR_EACH_PUBLIC_GC_POINTER_TYPE(DECLARE_IS_HEAP_CONSTRUCTIBLE_TYPE)
 FOR_EACH_PUBLIC_TAGGED_GC_POINTER_TYPE(DECLARE_IS_HEAP_CONSTRUCTIBLE_TYPE)
 #undef DECLARE_IS_HEAP_CONSTRUCTIBLE_TYPE
 
-template <typename T>
-class PersistentRootedBase {};
+template <typename T, typename Wrapper>
+class PersistentRootedBase : public MutableWrappedPtrOperations<T, Wrapper> {};
 
 static void* const ConstNullValue = nullptr;
 
@@ -143,10 +149,6 @@ template<typename T>
 struct PersistentRootedMarker;
 } /* namespace gc */
 
-#define DECLARE_POINTER_COMPARISON_OPS(T)                                                         \
-    bool operator==(const T& other) const { return get() == other; }                              \
-    bool operator!=(const T& other) const { return get() != other; }
-
 // Important: Return a reference so passing a Rooted<T>, etc. to
 // something that takes a |const T&| is not a GC hazard.
 #define DECLARE_POINTER_CONSTREF_OPS(T)                                                           \
@@ -230,12 +232,14 @@ AssertGCThingIsNotAnObjectSubclass(js::gc::Cell* cell) {}
  * Type T must be a public GC pointer type.
  */
 template <typename T>
-class MOZ_NON_MEMMOVABLE Heap : public js::HeapBase<T>
+class MOZ_NON_MEMMOVABLE Heap : public js::HeapBase<T, Heap<T>>
 {
     // Please note: this can actually also be used by nsXBLMaybeCompiled<T>, for legacy reasons.
     static_assert(js::IsHeapConstructibleType<T>::value,
                   "Type T must be a public GC pointer type");
   public:
+    using ElementType = T;
+
     Heap() {
         static_assert(sizeof(T) == sizeof(Heap<T>),
                       "Heap<T> must be binary compatible with T.");
@@ -367,9 +371,11 @@ ScriptIsMarkedGray(const Heap<JSScript*>& script)
  *  - It is not possible to store flag bits in a Heap<T>.
  */
 template <typename T>
-class TenuredHeap : public js::HeapBase<T>
+class TenuredHeap : public js::HeapBase<T, TenuredHeap<T>>
 {
   public:
+    using ElementType = T;
+
     TenuredHeap() : bits(0) {
         static_assert(sizeof(T) == sizeof(TenuredHeap<T>),
                       "TenuredHeap<T> must be binary compatible with T.");
@@ -377,9 +383,6 @@ class TenuredHeap : public js::HeapBase<T>
     explicit TenuredHeap(T p) : bits(0) { setPtr(p); }
     explicit TenuredHeap(const TenuredHeap<T>& p) : bits(0) { setPtr(p.getPtr()); }
 
-    bool operator==(const TenuredHeap<T>& other) { return bits == other.bits; }
-    bool operator!=(const TenuredHeap<T>& other) { return bits != other.bits; }
-
     void setPtr(T newPtr) {
         MOZ_ASSERT((reinterpret_cast<uintptr_t>(newPtr) & flagsMask) == 0);
         if (newPtr)
@@ -451,11 +454,13 @@ class TenuredHeap : public js::HeapBase<T>
  * specialization, define a HandleBase<T> specialization containing them.
  */
 template <typename T>
-class MOZ_NONHEAP_CLASS Handle : public js::HandleBase<T>
+class MOZ_NONHEAP_CLASS Handle : public js::HandleBase<T, Handle<T>>
 {
     friend class JS::MutableHandle<T>;
 
   public:
+    using ElementType = T;
+
     /* Creates a handle from a handle of a type convertible to T. */
     template <typename S>
     MOZ_IMPLICIT Handle(Handle<S> handle,
@@ -516,7 +521,6 @@ class MOZ_NONHEAP_CLASS Handle : public js::HandleBase<T>
     MOZ_IMPLICIT Handle(MutableHandle<S>& root,
                         typename mozilla::EnableIf<mozilla::IsConvertible<S, T>::value, int>::Type dummy = 0);
 
-    DECLARE_POINTER_COMPARISON_OPS(T);
     DECLARE_POINTER_CONSTREF_OPS(T);
     DECLARE_NONPOINTER_ACCESSOR_METHODS(*ptr);
 
@@ -540,9 +544,11 @@ class MOZ_NONHEAP_CLASS Handle : public js::HandleBase<T>
  * them.
  */
 template <typename T>
-class MOZ_STACK_CLASS MutableHandle : public js::MutableHandleBase<T>
+class MOZ_STACK_CLASS MutableHandle : public js::MutableHandleBase<T, MutableHandle<T>>
 {
   public:
+    using ElementType = T;
+
     inline MOZ_IMPLICIT MutableHandle(Rooted<T>* root);
     inline MOZ_IMPLICIT MutableHandle(PersistentRooted<T>* root);
 
@@ -753,7 +759,7 @@ namespace JS {
  * specialization, define a RootedBase<T> specialization containing them.
  */
 template <typename T>
-class MOZ_RAII Rooted : public js::RootedBase<T>
+class MOZ_RAII Rooted : public js::RootedBase<T, Rooted<T>>
 {
     inline void registerWithRootLists(js::RootedListHeads& roots) {
         this->stack = &roots[JS::MapTypeToRootKind<T>::kind];
@@ -775,6 +781,8 @@ class MOZ_RAII Rooted : public js::RootedBase<T>
     }
 
   public:
+    using ElementType = T;
+
     template <typename RootingContext>
     explicit Rooted(const RootingContext& cx)
       : ptr(GCPolicy<T>::initial())
@@ -807,7 +815,6 @@ class MOZ_RAII Rooted : public js::RootedBase<T>
         ptr = mozilla::Move(value);
     }
 
-    DECLARE_POINTER_COMPARISON_OPS(T);
     DECLARE_POINTER_CONSTREF_OPS(T);
     DECLARE_POINTER_ASSIGN_OPS(Rooted, T);
     DECLARE_NONPOINTER_ACCESSOR_METHODS(ptr);
@@ -853,8 +860,8 @@ namespace js {
  *   Rooted<StringObject*> rooted(cx, &obj->as<StringObject*>());
  *   Handle<StringObject*> h = rooted;
  */
-template <>
-class RootedBase<JSObject*>
+template <typename Container>
+class RootedBase<JSObject*, Container> : public MutableWrappedPtrOperations<JSObject*, Container>
 {
   public:
     template <class U>
@@ -871,8 +878,8 @@ class RootedBase<JSObject*>
  *   Rooted<StringObject*> rooted(cx, &obj->as<StringObject*>());
  *   Handle<StringObject*> h = rooted;
  */
-template <>
-class HandleBase<JSObject*>
+template <typename Container>
+class HandleBase<JSObject*, Container> : public WrappedPtrOperations<JSObject*, Container>
 {
   public:
     template <class U>
@@ -881,16 +888,17 @@ class HandleBase<JSObject*>
 
 /** Interface substitute for Rooted<T> which does not root the variable's memory. */
 template <typename T>
-class MOZ_RAII FakeRooted : public RootedBase<T>
+class MOZ_RAII FakeRooted : public RootedBase<T, FakeRooted<T>>
 {
   public:
+    using ElementType = T;
+
     template <typename CX>
     explicit FakeRooted(CX* cx) : ptr(JS::GCPolicy<T>::initial()) {}
 
     template <typename CX>
     FakeRooted(CX* cx, T initial) : ptr(initial) {}
 
-    DECLARE_POINTER_COMPARISON_OPS(T);
     DECLARE_POINTER_CONSTREF_OPS(T);
     DECLARE_POINTER_ASSIGN_OPS(FakeRooted, T);
     DECLARE_NONPOINTER_ACCESSOR_METHODS(ptr);
@@ -908,9 +916,11 @@ class MOZ_RAII FakeRooted : public RootedBase<T>
 
 /** Interface substitute for MutableHandle<T> which is not required to point to rooted memory. */
 template <typename T>
-class FakeMutableHandle : public js::MutableHandleBase<T>
+class FakeMutableHandle : public js::MutableHandleBase<T, FakeMutableHandle<T>>
 {
   public:
+    using ElementType = T;
+
     MOZ_IMPLICIT FakeMutableHandle(T* t) {
         ptr = t;
     }
@@ -1075,7 +1085,7 @@ MutableHandle<T>::MutableHandle(PersistentRooted<T>* root)
  * marked when the object itself is marked.
  */
 template<typename T>
-class PersistentRooted : public js::PersistentRootedBase<T>,
+class PersistentRooted : public js::RootedBase<T, PersistentRooted<T>>,
                          private mozilla::LinkedListElement<PersistentRooted<T>>
 {
     using ListBase = mozilla::LinkedListElement<PersistentRooted<T>>;
@@ -1101,6 +1111,8 @@ class PersistentRooted : public js::PersistentRootedBase<T>,
     js::RootLists& rootLists(js::ContextFriendFields* cx) = delete;
 
   public:
+    using ElementType = T;
+
     PersistentRooted() : ptr(GCPolicy<T>::initial()) {}
 
     template <typename RootingContext>
@@ -1154,7 +1166,6 @@ class PersistentRooted : public js::PersistentRootedBase<T>,
         }
     }
 
-    DECLARE_POINTER_COMPARISON_OPS(T);
     DECLARE_POINTER_CONSTREF_OPS(T);
     DECLARE_POINTER_ASSIGN_OPS(PersistentRooted, T);
     DECLARE_NONPOINTER_ACCESSOR_METHODS(ptr);
@@ -1191,6 +1202,8 @@ class JS_PUBLIC_API(ObjectPtr)
     Heap<JSObject*> value;
 
   public:
+    using ElementType = JSObject*;
+
     ObjectPtr() : value(nullptr) {}
 
     explicit ObjectPtr(JSObject* obj) : value(obj) {}
@@ -1240,10 +1253,10 @@ class JS_PUBLIC_API(ObjectPtr)
 
 namespace js {
 
-template <typename Outer, typename T, typename D>
-class UniquePtrOperations
+template <typename T, typename D, typename Container>
+class WrappedPtrOperations<UniquePtr<T, D>, Container>
 {
-    const UniquePtr<T, D>& uniquePtr() const { return static_cast<const Outer*>(this)->get(); }
+    const UniquePtr<T, D>& uniquePtr() const { return static_cast<const Container*>(this)->get(); }
 
   public:
     explicit operator bool() const { return !!uniquePtr(); }
@@ -1252,36 +1265,17 @@ class UniquePtrOperations
     T& operator*() const { return *uniquePtr(); }
 };
 
-template <typename Outer, typename T, typename D>
-class MutableUniquePtrOperations : public UniquePtrOperations<Outer, T, D>
+template <typename T, typename D, typename Container>
+class MutableWrappedPtrOperations<UniquePtr<T, D>, Container>
+  : public WrappedPtrOperations<UniquePtr<T, D>, Container>
 {
-    UniquePtr<T, D>& uniquePtr() { return static_cast<Outer*>(this)->get(); }
+    UniquePtr<T, D>& uniquePtr() { return static_cast<Container*>(this)->get(); }
 
   public:
     MOZ_MUST_USE typename UniquePtr<T, D>::Pointer release() { return uniquePtr().release(); }
     void reset(T* ptr = T()) { uniquePtr().reset(ptr); }
 };
 
-template <typename T, typename D>
-class RootedBase<UniquePtr<T, D>>
-  : public MutableUniquePtrOperations<JS::Rooted<UniquePtr<T, D>>, T, D>
-{ };
-
-template <typename T, typename D>
-class MutableHandleBase<UniquePtr<T, D>>
-  : public MutableUniquePtrOperations<JS::MutableHandle<UniquePtr<T, D>>, T, D>
-{ };
-
-template <typename T, typename D>
-class HandleBase<UniquePtr<T, D>>
-  : public UniquePtrOperations<JS::Handle<UniquePtr<T, D>>, T, D>
-{ };
-
-template <typename T, typename D>
-class PersistentRootedBase<UniquePtr<T, D>>
-  : public MutableUniquePtrOperations<JS::PersistentRooted<UniquePtr<T, D>>, T, D>
-{ };
-
 namespace gc {
 
 template <typename T, typename TraceCallbacks>
@@ -1324,6 +1318,177 @@ Swap(JS::TenuredHeap<T>& aX, JS::TenuredHeap<T>& aY)
 
 } /* namespace mozilla */
 
+namespace js {
+namespace detail {
+
+// DefineComparisonOps is a trait which selects which wrapper classes to define
+// operator== and operator!= for. It supplies a getter function to extract the
+// value to compare. This is used to avoid triggering the automatic read
+// barriers where appropriate.
+//
+// If DefineComparisonOps is not specialized for a particular wrapper you may
+// get errors such as 'invalid operands to binary expression' or 'no match for
+// operator==' when trying to compare against instances of the wrapper.
+
+template <typename T>
+struct DefineComparisonOps : mozilla::FalseType {};
+
+template <typename T>
+struct DefineComparisonOps<JS::Heap<T>> : mozilla::TrueType {
+    static const T& get(const JS::Heap<T>& v) { return v.unbarrieredGet(); }
+};
+
+template <typename T>
+struct DefineComparisonOps<JS::TenuredHeap<T>> : mozilla::TrueType {
+    static const T get(const JS::TenuredHeap<T>& v) { return v.unbarrieredGetPtr(); }
+};
+
+template <>
+struct DefineComparisonOps<JS::ObjectPtr> : mozilla::TrueType {
+    static const JSObject* get(const JS::ObjectPtr& v) { return v.unbarrieredGet(); }
+};
+
+template <typename T>
+struct DefineComparisonOps<JS::Rooted<T>> : mozilla::TrueType {
+    static const T& get(const JS::Rooted<T>& v) { return v.get(); }
+};
+
+template <typename T>
+struct DefineComparisonOps<JS::Handle<T>> : mozilla::TrueType {
+    static const T& get(const JS::Handle<T>& v) { return v.get(); }
+};
+
+template <typename T>
+struct DefineComparisonOps<JS::MutableHandle<T>> : mozilla::TrueType {
+    static const T& get(const JS::MutableHandle<T>& v) { return v.get(); }
+};
+
+template <typename T>
+struct DefineComparisonOps<JS::PersistentRooted<T>> : mozilla::TrueType {
+    static const T& get(const JS::PersistentRooted<T>& v) { return v.get(); }
+};
+
+template <typename T>
+struct DefineComparisonOps<js::FakeRooted<T>> : mozilla::TrueType {
+    static const T& get(const js::FakeRooted<T>& v) { return v.get(); }
+};
+
+template <typename T>
+struct DefineComparisonOps<js::FakeMutableHandle<T>> : mozilla::TrueType {
+    static const T& get(const js::FakeMutableHandle<T>& v) { return v.get(); }
+};
+
+} /* namespace detail */
+} /* namespace js */
+
+// Overload operator== and operator!= for all types with the DefineComparisonOps
+// trait using the supplied getter.
+//
+// There are four cases:
+
+// Case 1: comparison between two wrapper objects.
+
+template <typename T, typename U>
+typename mozilla::EnableIf<js::detail::DefineComparisonOps<T>::value &&
+                           js::detail::DefineComparisonOps<U>::value, bool>::Type
+operator==(const T& a, const U& b) {
+    return js::detail::DefineComparisonOps<T>::get(a) == js::detail::DefineComparisonOps<U>::get(b);
+}
+
+template <typename T, typename U>
+typename mozilla::EnableIf<js::detail::DefineComparisonOps<T>::value &&
+                           js::detail::DefineComparisonOps<U>::value, bool>::Type
+operator!=(const T& a, const U& b) {
+    return !(a == b);
+}
+
+// Case 2: comparison between a wrapper object and its unwrapped element type.
+
+template <typename T>
+typename mozilla::EnableIf<js::detail::DefineComparisonOps<T>::value, bool>::Type
+operator==(const T& a, const typename T::ElementType& b) {
+    return js::detail::DefineComparisonOps<T>::get(a) == b;
+}
+
+template <typename T>
+typename mozilla::EnableIf<js::detail::DefineComparisonOps<T>::value, bool>::Type
+operator!=(const T& a, const typename T::ElementType& b) {
+    return !(a == b);
+}
+
+template <typename T>
+typename mozilla::EnableIf<js::detail::DefineComparisonOps<T>::value, bool>::Type
+operator==(const typename T::ElementType& a, const T& b) {
+    return a == js::detail::DefineComparisonOps<T>::get(b);
+}
+
+template <typename T>
+typename mozilla::EnableIf<js::detail::DefineComparisonOps<T>::value, bool>::Type
+operator!=(const typename T::ElementType& a, const T& b) {
+    return !(a == b);
+}
+
+// Case 3: For pointer wrappers, comparison between the wrapper and a const
+// element pointer.
+
+template <typename T>
+typename mozilla::EnableIf<js::detail::DefineComparisonOps<T>::value &&
+                           mozilla::IsPointer<typename T::ElementType>::value, bool>::Type
+operator==(const typename mozilla::RemovePointer<typename T::ElementType>::Type* a, const T& b) {
+    return a == js::detail::DefineComparisonOps<T>::get(b);
+}
+
+template <typename T>
+typename mozilla::EnableIf<js::detail::DefineComparisonOps<T>::value &&
+                           mozilla::IsPointer<typename T::ElementType>::value, bool>::Type
+operator!=(const typename mozilla::RemovePointer<typename T::ElementType>::Type* a, const T& b) {
+    return !(a == b);
+}
+
+template <typename T>
+typename mozilla::EnableIf<js::detail::DefineComparisonOps<T>::value &&
+                           mozilla::IsPointer<typename T::ElementType>::value, bool>::Type
+operator==(const T& a, const typename mozilla::RemovePointer<typename T::ElementType>::Type* b) {
+    return js::detail::DefineComparisonOps<T>::get(a) == b;
+}
+
+template <typename T>
+typename mozilla::EnableIf<js::detail::DefineComparisonOps<T>::value &&
+                           mozilla::IsPointer<typename T::ElementType>::value, bool>::Type
+operator!=(const T& a, const typename mozilla::RemovePointer<typename T::ElementType>::Type* b) {
+    return !(a == b);
+}
+
+// Case 4: For pointer wrappers, comparison between the wrapper and nullptr.
+
+template <typename T>
+typename mozilla::EnableIf<js::detail::DefineComparisonOps<T>::value &&
+                           mozilla::IsPointer<typename T::ElementType>::value, bool>::Type
+operator==(std::nullptr_t a, const T& b) {
+    return a == js::detail::DefineComparisonOps<T>::get(b);
+}
+
+template <typename T>
+typename mozilla::EnableIf<js::detail::DefineComparisonOps<T>::value &&
+                           mozilla::IsPointer<typename T::ElementType>::value, bool>::Type
+operator!=(std::nullptr_t a, const T& b) {
+    return !(a == b);
+}
+
+template <typename T>
+typename mozilla::EnableIf<js::detail::DefineComparisonOps<T>::value &&
+                           mozilla::IsPointer<typename T::ElementType>::value, bool>::Type
+operator==(const T& a, std::nullptr_t b) {
+    return js::detail::DefineComparisonOps<T>::get(a) == b;
+}
+
+template <typename T>
+typename mozilla::EnableIf<js::detail::DefineComparisonOps<T>::value &&
+                           mozilla::IsPointer<typename T::ElementType>::value, bool>::Type
+operator!=(const T& a, std::nullptr_t b) {
+    return !(a == b);
+}
+
 #undef DELETE_ASSIGNMENT_OPS
 
 #endif  /* js_RootingAPI_h */
diff --git a/js/public/SweepingAPI.h b/js/public/SweepingAPI.h
index 39abb0fc0e..bbc1ec279b 100644
--- a/js/public/SweepingAPI.h
+++ b/js/public/SweepingAPI.h
@@ -8,11 +8,6 @@
 
 #include "js/HeapAPI.h"
 
-namespace js {
-template <typename T>
-class WeakCacheBase {};
-} // namespace js
-
 namespace JS {
 template <typename T> class WeakCache;
 
@@ -24,7 +19,7 @@ RegisterWeakCache(JS::Zone* zone, JS::WeakCache<void*>* cachep);
 // A WeakCache stores the given Sweepable container and links itself into a
 // list of such caches that are swept during each GC.
 template <typename T>
-class WeakCache : public js::WeakCacheBase<T>,
+class WeakCache : public js::MutableWrappedPtrOperations<T, WeakCache<T>>,
                   private mozilla::LinkedListElement<WeakCache<T>>
 {
     friend class mozilla::LinkedListElement<WeakCache<T>>;
diff --git a/js/public/Value.h b/js/public/Value.h
index 087d178efd..c645f07733 100644
--- a/js/public/Value.h
+++ b/js/public/Value.h
@@ -1340,20 +1340,18 @@ struct BarrierMethods<JS::Value>
     }
 };
 
-template <class Outer> class MutableValueOperations;
+template <class Wrapper> class MutableValueOperations;
 
 /**
  * A class designed for CRTP use in implementing the non-mutating parts of the
- * Value interface in Value-like classes.  Outer must be a class inheriting
- * ValueOperations<Outer> with a visible get() method returning a const
- * reference to the Value abstracted by Outer.
+ * Value interface in Value-like classes.  Wrapper must be a class inheriting
+ * ValueOperations<Wrapper> with a visible get() method returning a const
+ * reference to the Value abstracted by Wrapper.
  */
-template <class Outer>
-class ValueOperations
+template <class Wrapper>
+class WrappedPtrOperations<JS::Value, Wrapper>
 {
-    friend class MutableValueOperations<Outer>;
-
-    const JS::Value& value() const { return static_cast<const Outer*>(this)->get(); }
+    const JS::Value& value() const { return static_cast<const Wrapper*>(this)->get(); }
 
   public:
     bool isUndefined() const { return value().isUndefined(); }
@@ -1398,17 +1396,17 @@ class ValueOperations
 
 /**
  * A class designed for CRTP use in implementing all the mutating parts of the
- * Value interface in Value-like classes.  Outer must be a class inheriting
- * MutableValueOperations<Outer> with visible get() methods returning const and
- * non-const references to the Value abstracted by Outer.
+ * Value interface in Value-like classes.  Wrapper must be a class inheriting
+ * MutableWrappedPtrOperations<Wrapper> with visible get() methods returning const and
+ * non-const references to the Value abstracted by Wrapper.
  */
-template <class Outer>
-class MutableValueOperations : public ValueOperations<Outer>
+template <class Wrapper>
+class MutableWrappedPtrOperations<JS::Value, Wrapper> : public WrappedPtrOperations<JS::Value, Wrapper>
 {
   protected:
     void set(const JS::Value& v) {
       // Call Outer::set to trigger any barriers.
-      static_cast<Outer*>(this)->set(v);
+      static_cast<Wrapper*>(this)->set(v);
     }
 
   public:
@@ -1434,13 +1432,9 @@ class MutableValueOperations : public ValueOperations<Outer>
  * Augment the generic Heap<T> interface when T = Value with
  * type-querying, value-extracting, and mutating operations.
  */
-template <>
-class HeapBase<JS::Value> : public MutableValueOperations<JS::Heap<JS::Value> >
+template <typename Wrapper>
+class HeapBase<JS::Value, Wrapper> : public MutableWrappedPtrOperations<JS::Value, Wrapper>
 {
-    typedef JS::Heap<JS::Value> Outer;
-
-    friend class ValueOperations<Outer>;
-
   public:
     void setNumber(uint32_t ui) {
         if (ui > JSVAL_INT_MAX) {
@@ -1460,22 +1454,6 @@ class HeapBase<JS::Value> : public MutableValueOperations<JS::Heap<JS::Value> >
     }
 };
 
-template <>
-class HandleBase<JS::Value> : public ValueOperations<JS::Handle<JS::Value> >
-{};
-
-template <>
-class MutableHandleBase<JS::Value> : public MutableValueOperations<JS::MutableHandle<JS::Value> >
-{};
-
-template <>
-class RootedBase<JS::Value> : public MutableValueOperations<JS::Rooted<JS::Value> >
-{};
-
-template <>
-class PersistentRootedBase<JS::Value> : public MutableValueOperations<JS::PersistentRooted<JS::Value>>
-{};
-
 /*
  * If the Value is a GC pointer type, convert to that type and call |f| with
  * the pointer. If the Value is not a GC type, calls F::defaultValue.
diff --git a/js/src/NamespaceImports.h b/js/src/NamespaceImports.h
index de8e3a6f24..2b7a1f0e8b 100644
--- a/js/src/NamespaceImports.h
+++ b/js/src/NamespaceImports.h
@@ -45,6 +45,7 @@ class MOZ_STACK_CLASS SourceBufferHolder;
 class HandleValueArray;
 
 class ObjectOpResult;
+class PropertyResult;
 
 class Symbol;
 enum class SymbolCode: uint32_t;
@@ -150,6 +151,7 @@ using JS::FalseHandleValue;
 using JS::HandleValueArray;
 
 using JS::ObjectOpResult;
+using JS::PropertyResult;
 
 using JS::Zone;
 
diff --git a/js/src/builtin/MapObject.h b/js/src/builtin/MapObject.h
index 5382adfd25..a9f685ea00 100644
--- a/js/src/builtin/MapObject.h
+++ b/js/src/builtin/MapObject.h
@@ -52,14 +52,22 @@ class HashableValue
     }
 };
 
-template <>
-class RootedBase<HashableValue> {
+template <typename Wrapper>
+class WrappedPtrOperations<HashableValue, Wrapper>
+{
+  public:
+    Value value() const {
+        return static_cast<const Wrapper*>(this)->get().get();
+    }
+};
+
+template <typename Wrapper>
+class MutableWrappedPtrOperations<HashableValue, Wrapper>
+  : public WrappedPtrOperations<HashableValue, Wrapper>
+{
   public:
     MOZ_MUST_USE bool setValue(JSContext* cx, HandleValue v) {
-        return static_cast<JS::Rooted<HashableValue>*>(this)->get().setValue(cx, v);
-    }
-    Value value() const {
-        return static_cast<const JS::Rooted<HashableValue>*>(this)->get().get();
+        return static_cast<Wrapper*>(this)->get().setValue(cx, v);
     }
 };
 
diff --git a/js/src/builtin/Object.cpp b/js/src/builtin/Object.cpp
index 1221d2daf1..d661a222e5 100644
--- a/js/src/builtin/Object.cpp
+++ b/js/src/builtin/Object.cpp
@@ -69,18 +69,18 @@ js::obj_propertyIsEnumerable(JSContext* cx, unsigned argc, Value* vp)
         JSObject* obj = &args.thisv().toObject();
 
         /* Step 3. */
-        Shape* shape;
+        PropertyResult prop;
         if (obj->isNative() &&
-            NativeLookupOwnProperty<NoGC>(cx, &obj->as<NativeObject>(), id, &shape))
+            NativeLookupOwnProperty<NoGC>(cx, &obj->as<NativeObject>(), id, &prop))
         {
             /* Step 4. */
-            if (!shape) {
+            if (!prop) {
                 args.rval().setBoolean(false);
                 return true;
             }
 
             /* Step 5. */
-            unsigned attrs = GetShapeAttributes(obj, shape);
+            unsigned attrs = GetPropertyAttributes(obj, prop);
             args.rval().setBoolean((attrs & JSPROP_ENUMERATE) != 0);
             return true;
         }
@@ -582,11 +582,11 @@ js::obj_hasOwnProperty(JSContext* cx, unsigned argc, Value* vp)
     jsid id;
     if (args.thisv().isObject() && ValueToId<NoGC>(cx, idValue, &id)) {
         JSObject* obj = &args.thisv().toObject();
-        Shape* prop;
+        PropertyResult prop;
         if (obj->isNative() &&
             NativeLookupOwnProperty<NoGC>(cx, &obj->as<NativeObject>(), id, &prop))
         {
-            args.rval().setBoolean(!!prop);
+            args.rval().setBoolean(prop.isFound());
             return true;
         }
     }
@@ -839,7 +839,7 @@ EnumerableOwnProperties(JSContext* cx, const JS::CallArgs& args, EnumerableOwnPr
                 value = nobj->getDenseOrTypedArrayElement(JSID_TO_INT(id));
             } else {
                 shape = nobj->lookup(cx, id);
-                if (!shape || !(GetShapeAttributes(nobj, shape) & JSPROP_ENUMERATE))
+                if (!shape || !(shape->attributes() & JSPROP_ENUMERATE))
                     continue;
                 if (!shape->isAccessorShape()) {
                     if (!NativeGetExistingProperty(cx, nobj, nobj, shape, &value))
diff --git a/js/src/builtin/TypedObject.cpp b/js/src/builtin/TypedObject.cpp
index 4c938568f0..2796848c02 100644
--- a/js/src/builtin/TypedObject.cpp
+++ b/js/src/builtin/TypedObject.cpp
@@ -1671,10 +1671,10 @@ TypeDescr::hasProperty(const JSAtomState& names, jsid id)
 
 /* static */ bool
 TypedObject::obj_lookupProperty(JSContext* cx, HandleObject obj, HandleId id,
-                                MutableHandleObject objp, MutableHandleShape propp)
+                                MutableHandleObject objp, MutableHandle<PropertyResult> propp)
 {
     if (obj->as<TypedObject>().typeDescr().hasProperty(cx->names(), id)) {
-        MarkNonNativePropertyFound<CanGC>(propp);
+        propp.setNonNativeProperty();
         objp.set(obj);
         return true;
     }
@@ -1682,7 +1682,7 @@ TypedObject::obj_lookupProperty(JSContext* cx, HandleObject obj, HandleId id,
     RootedObject proto(cx, obj->staticPrototype());
     if (!proto) {
         objp.set(nullptr);
-        propp.set(nullptr);
+        propp.setNotFound();
         return true;
     }
 
diff --git a/js/src/builtin/TypedObject.h b/js/src/builtin/TypedObject.h
index 4fcd30cb0b..83700001d4 100644
--- a/js/src/builtin/TypedObject.h
+++ b/js/src/builtin/TypedObject.h
@@ -509,7 +509,7 @@ class TypedObject : public ShapedObject
 
     static MOZ_MUST_USE bool obj_lookupProperty(JSContext* cx, HandleObject obj,
                                                 HandleId id, MutableHandleObject objp,
-                                                MutableHandleShape propp);
+                                                MutableHandle<PropertyResult> propp);
 
     static MOZ_MUST_USE bool obj_defineProperty(JSContext* cx, HandleObject obj, HandleId id,
                                                 Handle<PropertyDescriptor> desc,
diff --git a/js/src/ds/TraceableFifo.h b/js/src/ds/TraceableFifo.h
index 04f67da151..0f94b93cbd 100644
--- a/js/src/ds/TraceableFifo.h
+++ b/js/src/ds/TraceableFifo.h
@@ -51,11 +51,11 @@ class TraceableFifo : public js::Fifo<T, MinInlineCapacity, AllocPolicy>
     }
 };
 
-template <typename Outer, typename T, size_t Capacity, typename AllocPolicy>
-class TraceableFifoOperations
+template <typename Wrapper, typename T, size_t Capacity, typename AllocPolicy>
+class WrappedPtrOperations<TraceableFifo<T, Capacity, AllocPolicy>, Wrapper>
 {
     using TF = TraceableFifo<T, Capacity, AllocPolicy>;
-    const TF& fifo() const { return static_cast<const Outer*>(this)->extract(); }
+    const TF& fifo() const { return static_cast<const Wrapper*>(this)->get(); }
 
   public:
     size_t length() const { return fifo().length(); }
@@ -63,12 +63,12 @@ class TraceableFifoOperations
     const T& front() const { return fifo().front(); }
 };
 
-template <typename Outer, typename T, size_t Capacity, typename AllocPolicy>
-class MutableTraceableFifoOperations
-  : public TraceableFifoOperations<Outer, T, Capacity, AllocPolicy>
+template <typename Wrapper, typename T, size_t Capacity, typename AllocPolicy>
+class MutableWrappedPtrOperations<TraceableFifo<T, Capacity, AllocPolicy>, Wrapper>
+  : public WrappedPtrOperations<TraceableFifo<T, Capacity, AllocPolicy>, Wrapper>
 {
     using TF = TraceableFifo<T, Capacity, AllocPolicy>;
-    TF& fifo() { return static_cast<Outer*>(this)->extract(); }
+    TF& fifo() { return static_cast<Wrapper*>(this)->get(); }
 
   public:
     T& front() { return fifo().front(); }
@@ -82,46 +82,6 @@ class MutableTraceableFifoOperations
     void clear() { fifo().clear(); }
 };
 
-template <typename A, size_t B, typename C>
-class RootedBase<TraceableFifo<A,B,C>>
-  : public MutableTraceableFifoOperations<JS::Rooted<TraceableFifo<A,B,C>>, A,B,C>
-{
-    using TF = TraceableFifo<A,B,C>;
-
-    friend class TraceableFifoOperations<JS::Rooted<TF>, A,B,C>;
-    const TF& extract() const { return *static_cast<const JS::Rooted<TF>*>(this)->address(); }
-
-    friend class MutableTraceableFifoOperations<JS::Rooted<TF>, A,B,C>;
-    TF& extract() { return *static_cast<JS::Rooted<TF>*>(this)->address(); }
-};
-
-template <typename A, size_t B, typename C>
-class MutableHandleBase<TraceableFifo<A,B,C>>
-  : public MutableTraceableFifoOperations<JS::MutableHandle<TraceableFifo<A,B,C>>, A,B,C>
-{
-    using TF = TraceableFifo<A,B,C>;
-
-    friend class TraceableFifoOperations<JS::MutableHandle<TF>, A,B,C>;
-    const TF& extract() const {
-        return *static_cast<const JS::MutableHandle<TF>*>(this)->address();
-    }
-
-    friend class MutableTraceableFifoOperations<JS::MutableHandle<TF>, A,B,C>;
-    TF& extract() { return *static_cast<JS::MutableHandle<TF>*>(this)->address(); }
-};
-
-template <typename A, size_t B, typename C>
-class HandleBase<TraceableFifo<A,B,C>>
-  : public TraceableFifoOperations<JS::Handle<TraceableFifo<A,B,C>>, A,B,C>
-{
-    using TF = TraceableFifo<A,B,C>;
-
-    friend class TraceableFifoOperations<JS::Handle<TF>, A,B,C>;
-    const TF& extract() const {
-        return *static_cast<const JS::Handle<TF>*>(this)->address();
-    }
-};
-
 } // namespace js
 
 #endif // js_TraceableFifo_h
diff --git a/js/src/gc/Barrier.h b/js/src/gc/Barrier.h
index 681ccc9c4c..345131a296 100644
--- a/js/src/gc/Barrier.h
+++ b/js/src/gc/Barrier.h
@@ -261,8 +261,6 @@ struct InternalBarrierMethods<T*>
 {
     static bool isMarkable(T* v) { return v != nullptr; }
 
-    static bool isMarkableTaggedPointer(T* v) { return !IsNullTaggedPointer(v); }
-
     static void preBarrier(T* v) { T::writeBarrierPre(v); }
 
     static void postBarrier(T** vp, T* prev, T* next) { T::writeBarrierPost(vp, prev, next); }
@@ -282,7 +280,6 @@ template <>
 struct InternalBarrierMethods<Value>
 {
     static bool isMarkable(const Value& v) { return v.isGCThing(); }
-    static bool isMarkableTaggedPointer(const Value& v) { return isMarkable(v); }
 
     static void preBarrier(const Value& v) {
         DispatchTyped(PreBarrierFunctor<Value>(), v);
@@ -318,24 +315,17 @@ template <>
 struct InternalBarrierMethods<jsid>
 {
     static bool isMarkable(jsid id) { return JSID_IS_GCTHING(id); }
-    static bool isMarkableTaggedPointer(jsid id) { return isMarkable(id); }
 
     static void preBarrier(jsid id) { DispatchTyped(PreBarrierFunctor<jsid>(), id); }
     static void postBarrier(jsid* idp, jsid prev, jsid next) {}
 };
 
-// Barrier classes can use Mixins to add methods to a set of barrier
-// instantiations, to make the barriered thing look and feel more like the
-// thing itself.
-template <typename T>
-class BarrieredBaseMixins {};
-
 // Base class of all barrier types.
 //
 // This is marked non-memmovable since post barriers added by derived classes
 // can add pointers to class instances to the store buffer.
 template <typename T>
-class MOZ_NON_MEMMOVABLE BarrieredBase : public BarrieredBaseMixins<T>
+class MOZ_NON_MEMMOVABLE BarrieredBase
 {
   protected:
     // BarrieredBase is not directly instantiable.
@@ -356,14 +346,18 @@ class MOZ_NON_MEMMOVABLE BarrieredBase : public BarrieredBaseMixins<T>
 
 // Base class for barriered pointer types that intercept only writes.
 template <class T>
-class WriteBarrieredBase : public BarrieredBase<T>
+class WriteBarrieredBase : public BarrieredBase<T>,
+                           public WrappedPtrOperations<T, WriteBarrieredBase<T>>
 {
   protected:
+    using BarrieredBase<T>::value;
+
     // WriteBarrieredBase is not directly instantiable.
     explicit WriteBarrieredBase(const T& v) : BarrieredBase<T>(v) {}
 
   public:
-    DECLARE_POINTER_COMPARISON_OPS(T);
+    using ElementType = T;
+
     DECLARE_POINTER_CONSTREF_OPS(T);
 
     // Use this if the automatic coercion to T isn't working.
@@ -460,10 +454,6 @@ class GCPtr : public WriteBarrieredBase<T>
 
     DECLARE_POINTER_ASSIGN_OPS(GCPtr, T);
 
-    T unbarrieredGet() const {
-        return this->value;
-    }
-
   private:
     void set(const T& v) {
         this->pre();
@@ -580,8 +570,12 @@ class ReadBarrieredBase : public BarrieredBase<T>
 // insert manual post-barriers on the table for rekeying if the key is based in
 // any way on the address of the object.
 template <typename T>
-class ReadBarriered : public ReadBarrieredBase<T>
+class ReadBarriered : public ReadBarrieredBase<T>,
+                      public WrappedPtrOperations<T, ReadBarriered<T>>
 {
+  protected:
+    using ReadBarrieredBase<T>::value;
+
   public:
     ReadBarriered() : ReadBarrieredBase<T>(JS::GCPolicy<T>::initial()) {}
 
@@ -614,14 +608,13 @@ class ReadBarriered : public ReadBarrieredBase<T>
         return *this;
     }
 
-    const T get() const {
-        if (!InternalBarrierMethods<T>::isMarkable(this->value))
-            return JS::GCPolicy<T>::initial();
-        this->read();
+    const T& get() const {
+        if (InternalBarrierMethods<T>::isMarkable(this->value))
+            this->read();
         return this->value;
     }
 
-    const T unbarrieredGet() const {
+    const T& unbarrieredGet() const {
         return this->value;
     }
 
@@ -629,9 +622,9 @@ class ReadBarriered : public ReadBarrieredBase<T>
         return bool(this->value);
     }
 
-    operator const T() const { return get(); }
+    operator const T&() const { return get(); }
 
-    const T operator->() const { return get(); }
+    const T& operator->() const { return get(); }
 
     T* unsafeGet() { return &this->value; }
     T const* unsafeGet() const { return &this->value; }
@@ -649,12 +642,6 @@ class ReadBarriered : public ReadBarrieredBase<T>
 template <typename T>
 using WeakRef = ReadBarriered<T>;
 
-// Add Value operations to all Barrier types. Note, this must be defined before
-// HeapSlot for HeapSlot's base to get these operations.
-template <>
-class BarrieredBaseMixins<JS::Value> : public ValueOperations<WriteBarrieredBase<JS::Value>>
-{};
-
 // A pre- and post-barriered Value that is specialized to be aware that it
 // resides in a slots or elements vector. This allows it to be relocated in
 // memory, but with substantially less overhead than a HeapPtr.
@@ -943,6 +930,36 @@ typedef ReadBarriered<WasmTableObject*> ReadBarrieredWasmTableObject;
 
 typedef ReadBarriered<Value> ReadBarrieredValue;
 
+namespace detail {
+
+template <typename T>
+struct DefineComparisonOps<PreBarriered<T>> : mozilla::TrueType {
+    static const T& get(const PreBarriered<T>& v) { return v.get(); }
+};
+
+template <typename T>
+struct DefineComparisonOps<GCPtr<T>> : mozilla::TrueType {
+    static const T& get(const GCPtr<T>& v) { return v.get(); }
+};
+
+template <typename T>
+struct DefineComparisonOps<HeapPtr<T>> : mozilla::TrueType {
+    static const T& get(const HeapPtr<T>& v) { return v.get(); }
+};
+
+template <typename T>
+struct DefineComparisonOps<ReadBarriered<T>> : mozilla::TrueType {
+    static const T& get(const ReadBarriered<T>& v) { return v.unbarrieredGet(); }
+};
+
+template <>
+struct DefineComparisonOps<HeapSlot> : mozilla::TrueType {
+    static const Value& get(const HeapSlot& v) { return v.get(); }
+};
+
+} /* namespace detail */
+
+
 } /* namespace js */
 
 #endif /* gc_Barrier_h */
diff --git a/js/src/gc/Heap.h b/js/src/gc/Heap.h
index 2f27702601..ce4a0dbd56 100644
--- a/js/src/gc/Heap.h
+++ b/js/src/gc/Heap.h
@@ -317,10 +317,6 @@ class TenuredCell : public Cell
     MOZ_ALWAYS_INLINE void unmark(uint32_t color) const;
     MOZ_ALWAYS_INLINE void copyMarkBitsFrom(const TenuredCell* src);
 
-    // Note: this is in TenuredCell because JSObject subclasses are sometimes
-    // used tagged.
-    static MOZ_ALWAYS_INLINE bool isNullLike(const Cell* thing) { return !thing; }
-
     // Access to the arena.
     inline Arena* arena() const;
     inline AllocKind getAllocKind() const;
@@ -1302,7 +1298,7 @@ TenuredCell::isInsideZone(JS::Zone* zone) const
 TenuredCell::readBarrier(TenuredCell* thing)
 {
     MOZ_ASSERT(!CurrentThreadIsIonCompiling());
-    MOZ_ASSERT(!isNullLike(thing));
+    MOZ_ASSERT(thing);
 
     // It would be good if barriers were never triggered during collection, but
     // at the moment this can happen e.g. when rekeying tables containing
@@ -1335,7 +1331,6 @@ AssertSafeToSkipBarrier(TenuredCell* thing);
 TenuredCell::writeBarrierPre(TenuredCell* thing)
 {
     MOZ_ASSERT(!CurrentThreadIsIonCompiling());
-    MOZ_ASSERT_IF(thing, !isNullLike(thing));
     if (!thing)
         return;
 
diff --git a/js/src/gc/Marking.cpp b/js/src/gc/Marking.cpp
index 241a1df20d..da8da5c6b5 100644
--- a/js/src/gc/Marking.cpp
+++ b/js/src/gc/Marking.cpp
@@ -501,7 +501,7 @@ void
 js::TraceNullableRoot(JSTracer* trc, T* thingp, const char* name)
 {
     AssertRootMarkingPhase(trc);
-    if (InternalBarrierMethods<T>::isMarkableTaggedPointer(*thingp))
+    if (InternalBarrierMethods<T>::isMarkable(*thingp))
         DispatchToTracer(trc, ConvertToBase(thingp), name);
 }
 
diff --git a/js/src/gc/Marking.h b/js/src/gc/Marking.h
index 2b9e7ace1f..40b331b311 100644
--- a/js/src/gc/Marking.h
+++ b/js/src/gc/Marking.h
@@ -414,14 +414,6 @@ ToMarkable(Cell* cell)
     return cell;
 }
 
-// Return true if the pointer is nullptr, or if it is a tagged pointer to
-// nullptr.
-MOZ_ALWAYS_INLINE bool
-IsNullTaggedPointer(void* p)
-{
-    return uintptr_t(p) <= LargestTaggedNullCellPointer;
-}
-
 // Wrap a GC thing pointer into a new Value or jsid. The type system enforces
 // that the thing pointer is a wrappable type.
 template <typename S, typename T>
diff --git a/js/src/jit/BaselineIC.cpp b/js/src/jit/BaselineIC.cpp
index f5dcd2a106..7dbe239a7e 100644
--- a/js/src/jit/BaselineIC.cpp
+++ b/js/src/jit/BaselineIC.cpp
@@ -1145,9 +1145,9 @@ TryAttachNativeOrUnboxedGetValueElemStub(JSContext* cx, HandleScript script, jsb
         return true;
     bool needsAtomize = checkAtomize<T>(keyVal);
 
-    RootedShape shape(cx);
+    Rooted<PropertyResult> prop(cx);
     RootedObject holder(cx);
-    if (!EffectlesslyLookupProperty(cx, obj, id, &holder, &shape))
+    if (!EffectlesslyLookupProperty(cx, obj, id, &holder, &prop))
         return false;
     if (!holder || (holder != obj && !holder->isNative()))
         return true;
@@ -1214,6 +1214,8 @@ TryAttachNativeOrUnboxedGetValueElemStub(JSContext* cx, HandleScript script, jsb
     if (!holder->isNative())
         return true;
 
+    RootedShape shape(cx, prop.shape());
+
     if (IsCacheableGetPropReadSlot(obj, holder, shape)) {
         bool isFixedSlot;
         uint32_t offset;
@@ -1264,13 +1266,14 @@ TryAttachNativeGetAccessorElemStub(JSContext* cx, HandleScript script, jsbytecod
         return true;
     bool needsAtomize = checkAtomize<T>(keyVal);
 
-    RootedShape shape(cx);
+    Rooted<PropertyResult> prop(cx);
     RootedObject baseHolder(cx);
-    if (!EffectlesslyLookupProperty(cx, obj, id, &baseHolder, &shape))
+    if (!EffectlesslyLookupProperty(cx, obj, id, &baseHolder, &prop))
         return false;
     if (!baseHolder || !baseHolder->isNative())
         return true;
 
+    RootedShape shape(cx, prop.shape());
     HandleNativeObject holder = baseHolder.as<NativeObject>();
 
     bool getterIsScripted = false;
@@ -3348,11 +3351,17 @@ TryAttachNativeInStub(JSContext* cx, HandleScript outerScript, ICIn_Fallback* st
         return true;
 
     RootedPropertyName name(cx, JSID_TO_ATOM(id)->asPropertyName());
-    RootedShape shape(cx);
+    Rooted<PropertyResult> prop(cx);
     RootedObject holder(cx);
-    if (!EffectlesslyLookupProperty(cx, obj, id, &holder, &shape))
+    if (!EffectlesslyLookupProperty(cx, obj, id, &holder, &prop))
         return false;
 
+    if (prop.isNonNativeProperty()) {
+        MOZ_ASSERT(!IsCacheableProtoChain(obj, holder, false));
+        return true;
+    }
+
+    RootedShape shape(cx, prop.maybeShape());
     if (IsCacheableGetPropReadSlot(obj, holder, shape)) {
         ICStub::Kind kind = (obj == holder) ? ICStub::In_Native
                                             : ICStub::In_NativePrototype;
@@ -4259,14 +4268,17 @@ TryAttachSetValuePropStub(JSContext* cx, HandleScript script, jsbytecode* pc, IC
 {
     MOZ_ASSERT(!*attached);
 
-    RootedShape shape(cx);
+    Rooted<PropertyResult> prop(cx);
     RootedObject holder(cx);
-    if (!EffectlesslyLookupProperty(cx, obj, id, &holder, &shape))
+    if (!EffectlesslyLookupProperty(cx, obj, id, &holder, &prop))
         return false;
     if (obj != holder)
         return true;
 
-    if (!obj->isNative()) {
+    RootedShape shape(cx);
+    if (obj->isNative()) {
+        shape = prop.shape();
+    } else {
         if (obj->is<UnboxedPlainObject>()) {
             UnboxedExpandoObject* expando = obj->as<UnboxedPlainObject>().maybeExpando();
             if (expando) {
@@ -4365,11 +4377,17 @@ TryAttachSetAccessorPropStub(JSContext* cx, HandleScript script, jsbytecode* pc,
     MOZ_ASSERT(!*attached);
     MOZ_ASSERT(!*isTemporarilyUnoptimizable);
 
-    RootedShape shape(cx);
+    Rooted<PropertyResult> prop(cx);
     RootedObject holder(cx);
-    if (!EffectlesslyLookupProperty(cx, obj, id, &holder, &shape))
+    if (!EffectlesslyLookupProperty(cx, obj, id, &holder, &prop))
         return false;
 
+    if (prop.isNonNativeProperty()) {
+        MOZ_ASSERT(!IsCacheableProtoChain(obj, holder));
+        return true;
+    }
+
+    RootedShape shape(cx, prop.maybeShape());
     bool isScripted = false;
     bool cacheableCall = IsCacheableSetPropCall(cx, obj, holder, shape,
                                                 &isScripted, isTemporarilyUnoptimizable);
diff --git a/js/src/jit/CacheIR.cpp b/js/src/jit/CacheIR.cpp
index fc58bdb98e..9168a344e5 100644
--- a/js/src/jit/CacheIR.cpp
+++ b/js/src/jit/CacheIR.cpp
@@ -109,7 +109,8 @@ CanAttachNativeGetProp(JSContext* cx, HandleObject obj, HandleId id,
     // only miss out on shape hashification, which is only a temporary perf cost.
     // The limits were arbitrarily set, anyways.
     JSObject* baseHolder = nullptr;
-    if (!LookupPropertyPure(cx, obj, id, &baseHolder, shape.address()))
+    PropertyResult prop;
+    if (!LookupPropertyPure(cx, obj, id, &baseHolder, &prop))
         return CanAttachNone;
 
     MOZ_ASSERT(!holder);
@@ -118,8 +119,9 @@ CanAttachNativeGetProp(JSContext* cx, HandleObject obj, HandleId id,
             return CanAttachNone;
         holder.set(&baseHolder->as<NativeObject>());
     }
+    shape.set(prop.maybeShape());
 
-    if (IsCacheableGetPropReadSlotForIonOrCacheIR(obj, holder, shape) ||
+    if (IsCacheableGetPropReadSlotForIonOrCacheIR(obj, holder, prop) ||
         IsCacheableNoProperty(cx, obj, holder, shape, id, pc))
     {
         return CanAttachReadSlot;
diff --git a/js/src/jit/IonCaches.cpp b/js/src/jit/IonCaches.cpp
index 0a0c7ac22e..5a7e437285 100644
--- a/js/src/jit/IonCaches.cpp
+++ b/js/src/jit/IonCaches.cpp
@@ -468,11 +468,12 @@ jit::IsCacheableProtoChainForIonOrCacheIR(JSObject* obj, JSObject* holder)
 }
 
 bool
-jit::IsCacheableGetPropReadSlotForIonOrCacheIR(JSObject* obj, JSObject* holder, Shape* shape)
+jit::IsCacheableGetPropReadSlotForIonOrCacheIR(JSObject* obj, JSObject* holder, PropertyResult prop)
 {
-    if (!shape || !IsCacheableProtoChainForIonOrCacheIR(obj, holder))
+    if (!prop || !IsCacheableProtoChainForIonOrCacheIR(obj, holder))
         return false;
 
+    Shape* shape = prop.shape();
     if (!shape->hasSlot() || !shape->hasDefaultGetter())
         return false;
 
@@ -480,10 +481,10 @@ jit::IsCacheableGetPropReadSlotForIonOrCacheIR(JSObject* obj, JSObject* holder,
 }
 
 static bool
-IsCacheableNoProperty(JSObject* obj, JSObject* holder, Shape* shape, jsbytecode* pc,
+IsCacheableNoProperty(JSObject* obj, JSObject* holder, PropertyResult prop, jsbytecode* pc,
                       const TypedOrValueRegister& output)
 {
-    if (shape)
+    if (prop)
         return false;
 
     MOZ_ASSERT(!holder);
@@ -751,7 +752,7 @@ CheckDOMProxyExpandoDoesNotShadow(JSContext* cx, MacroAssembler& masm, JSObject*
 static void
 GenerateReadSlot(JSContext* cx, IonScript* ion, MacroAssembler& masm,
                  IonCache::StubAttacher& attacher, MaybeCheckTDZ checkTDZ,
-                 JSObject* obj, JSObject* holder, Shape* shape, Register object,
+                 JSObject* obj, JSObject* holder, PropertyResult prop, Register object,
                  TypedOrValueRegister output, Label* failures = nullptr)
 {
     // If there's a single jump to |failures|, we can patch the shape guard
@@ -778,7 +779,7 @@ GenerateReadSlot(JSContext* cx, IonScript* ion, MacroAssembler& masm,
 
     if (obj != holder ||
         obj->is<UnboxedPlainObject>() ||
-        !holder->as<NativeObject>().isFixedSlot(shape->slot()))
+        !holder->as<NativeObject>().isFixedSlot(prop.shape()->slot()))
     {
         if (output.hasValue()) {
             scratchReg = output.valueReg().scratchReg();
@@ -793,7 +794,7 @@ GenerateReadSlot(JSContext* cx, IonScript* ion, MacroAssembler& masm,
 
     // Fast path: single failure jump, no prototype guards.
     if (!multipleFailureJumps) {
-        EmitLoadSlot(masm, &holder->as<NativeObject>(), shape, object, output, scratchReg);
+        EmitLoadSlot(masm, &holder->as<NativeObject>(), prop.shape(), object, output, scratchReg);
         if (restoreScratch)
             masm.pop(scratchReg);
         attacher.jumpRejoin(masm);
@@ -848,7 +849,8 @@ GenerateReadSlot(JSContext* cx, IonScript* ion, MacroAssembler& masm,
 
     // Slot access.
     if (holder) {
-        EmitLoadSlot(masm, &holder->as<NativeObject>(), shape, holderReg, output, scratchReg);
+        EmitLoadSlot(masm, &holder->as<NativeObject>(), prop.shape(), holderReg, output,
+                     scratchReg);
         if (checkTDZ && output.hasValue())
             masm.branchTestMagic(Assembler::Equal, output.valueReg(), failures);
     } else {
@@ -1294,7 +1296,8 @@ CanAttachNativeGetProp(JSContext* cx, const GetPropCache& cache,
     // only miss out on shape hashification, which is only a temporary perf cost.
     // The limits were arbitrarily set, anyways.
     JSObject* baseHolder = nullptr;
-    if (!LookupPropertyPure(cx, obj, id, &baseHolder, shape.address()))
+    PropertyResult prop;
+    if (!LookupPropertyPure(cx, obj, id, &baseHolder, &prop))
         return GetPropertyIC::CanAttachNone;
 
     MOZ_ASSERT(!holder);
@@ -1303,12 +1306,13 @@ CanAttachNativeGetProp(JSContext* cx, const GetPropCache& cache,
             return GetPropertyIC::CanAttachNone;
         holder.set(&baseHolder->as<NativeObject>());
     }
+    shape.set(prop.maybeShape());
 
     RootedScript script(cx);
     jsbytecode* pc;
     cache.getScriptedLocation(&script, &pc);
-    if (IsCacheableGetPropReadSlotForIonOrCacheIR(obj, holder, shape) ||
-        IsCacheableNoProperty(obj, holder, shape, pc, cache.output()))
+    if (IsCacheableGetPropReadSlotForIonOrCacheIR(obj, holder, prop) ||
+        IsCacheableNoProperty(obj, holder, prop, pc, cache.output()))
     {
         return GetPropertyIC::CanAttachReadSlot;
     }
@@ -1505,7 +1509,7 @@ GetPropertyIC::tryAttachNative(JSContext* cx, HandleScript outerScript, IonScrip
     switch (type) {
       case CanAttachReadSlot:
         GenerateReadSlot(cx, ion, masm, attacher, DontCheckTDZ, obj, holder,
-                         shape, object(), output(), maybeFailures);
+                         PropertyResult(shape), object(), output(), maybeFailures);
         attachKind = idempotent() ? "idempotent reading"
                                     : "non idempotent reading";
         outcome = JS::TrackedOutcome::ICGetPropStub_ReadSlot;
@@ -1588,7 +1592,7 @@ GetPropertyIC::tryAttachUnboxedExpando(JSContext* cx, HandleScript outerScript,
 
     StubAttacher attacher(*this);
     GenerateReadSlot(cx, ion, masm, attacher, DontCheckTDZ, obj, obj,
-                     shape, object(), output(), maybeFailures);
+                     PropertyResult(shape), object(), output(), maybeFailures);
     return linkAndAttachStub(cx, masm, attacher, ion, "read unboxed expando",
                              JS::TrackedOutcome::ICGetPropStub_UnboxedReadExpando);
 }
@@ -2927,12 +2931,14 @@ IsCacheableDOMProxyUnshadowedSetterCall(JSContext* cx, HandleObject obj, HandleI
     if (!checkObj)
         return false;
 
-    if (!LookupPropertyPure(cx, obj, id, holder.address(), shape.address()))
+    PropertyResult prop;
+    if (!LookupPropertyPure(cx, obj, id, holder.address(), &prop))
         return false;
 
-    if (!holder)
+    if (!holder || !holder->isNative())
         return false;
 
+    shape.set(prop.shape());
     return IsCacheableSetPropCallNative(checkObj, holder, shape) ||
            IsCacheableSetPropCallPropertyOp(checkObj, holder, shape) ||
            IsCacheableSetPropCallScripted(checkObj, holder, shape);
@@ -3344,22 +3350,26 @@ CanAttachNativeSetProp(JSContext* cx, HandleObject obj, HandleId id, const Const
 
     // If we couldn't find the property on the object itself, do a full, but
     // still pure lookup for setters.
-    if (!LookupPropertyPure(cx, obj, id, holder.address(), shape.address()))
+    Rooted<PropertyResult> prop(cx);
+    if (!LookupPropertyPure(cx, obj, id, holder.address(), prop.address()))
         return SetPropertyIC::CanAttachNone;
 
     // If the object doesn't have the property, we don't know if we can attach
     // a stub to add the property until we do the VM call to add. If the
     // property exists as a data property on the prototype, we should add
     // a new, shadowing property.
-    if (obj->isNative() && (!shape || (obj != holder && holder->isNative() &&
-                                       shape->hasDefaultSetter() && shape->hasSlot())))
+    if (obj->isNative() &&
+        (!prop || (obj != holder && holder->isNative() &&
+                   prop.shape()->hasDefaultSetter() && prop.shape()->hasSlot())))
     {
+        shape.set(prop.maybeShape());
         return SetPropertyIC::MaybeCanAttachAddSlot;
     }
 
-    if (IsImplicitNonNativeProperty(shape))
+    if (prop.isNonNativeProperty())
         return SetPropertyIC::CanAttachNone;
 
+    shape.set(prop.maybeShape());
     if (IsCacheableSetPropCallPropertyOp(obj, holder, shape) ||
         IsCacheableSetPropCallNative(obj, holder, shape) ||
         IsCacheableSetPropCallScripted(obj, holder, shape))
@@ -4836,7 +4846,7 @@ BindNameIC::update(JSContext* cx, HandleScript outerScript, size_t cacheIndex,
 bool
 NameIC::attachReadSlot(JSContext* cx, HandleScript outerScript, IonScript* ion,
                        HandleObject envChain, HandleObject holderBase,
-                       HandleNativeObject holder, HandleShape shape)
+                       HandleNativeObject holder, Handle<PropertyResult> prop)
 {
     MacroAssembler masm(cx, ion, outerScript, profilerLeavePc_);
     Label failures;
@@ -4854,7 +4864,7 @@ NameIC::attachReadSlot(JSContext* cx, HandleScript outerScript, IonScript* ion,
     // doesn't generate the extra guard.
     //
     // NAME ops must do their own TDZ checks.
-    GenerateReadSlot(cx, ion, masm, attacher, CheckTDZ, holderBase, holder, shape, scratchReg,
+    GenerateReadSlot(cx, ion, masm, attacher, CheckTDZ, holderBase, holder, prop, scratchReg,
                      outputReg(), failures.used() ? &failures : nullptr);
 
     return linkAndAttachStub(cx, masm, attacher, ion, "generic",
@@ -4880,26 +4890,26 @@ IsCacheableEnvironmentChain(JSObject* envChain, JSObject* obj)
 }
 
 static bool
-IsCacheableNameReadSlot(HandleObject envChain, HandleObject obj,
-                        HandleObject holder, HandleShape shape, jsbytecode* pc,
+IsCacheableNameReadSlot(JSContext* cx, HandleObject envChain, HandleObject obj,
+                        HandleObject holder, Handle<PropertyResult> prop, jsbytecode* pc,
                         const TypedOrValueRegister& output)
 {
-    if (!shape)
+    if (!prop)
         return false;
     if (!obj->isNative())
         return false;
 
     if (obj->is<GlobalObject>()) {
         // Support only simple property lookups.
-        if (!IsCacheableGetPropReadSlotForIonOrCacheIR(obj, holder, shape) &&
-            !IsCacheableNoProperty(obj, holder, shape, pc, output))
+        if (!IsCacheableGetPropReadSlotForIonOrCacheIR(obj, holder, prop) &&
+            !IsCacheableNoProperty(obj, holder, prop, pc, output))
             return false;
     } else if (obj->is<ModuleEnvironmentObject>()) {
         // We don't yet support lookups in a module environment.
         return false;
     } else if (obj->is<CallObject>()) {
         MOZ_ASSERT(obj == holder);
-        if (!shape->hasDefaultGetter())
+        if (!prop.shape()->hasDefaultGetter())
             return false;
     } else {
         // We don't yet support lookups on Block or DeclEnv objects.
@@ -4942,9 +4952,9 @@ NameIC::attachCallGetter(JSContext* cx, HandleScript outerScript, IonScript* ion
 
 static bool
 IsCacheableNameCallGetter(HandleObject envChain, HandleObject obj, HandleObject holder,
-                          HandleShape shape)
+                          Handle<PropertyResult> prop)
 {
-    if (!shape)
+    if (!prop)
         return false;
     if (!obj->is<GlobalObject>())
         return false;
@@ -4952,6 +4962,10 @@ IsCacheableNameCallGetter(HandleObject envChain, HandleObject obj, HandleObject
     if (!IsCacheableEnvironmentChain(envChain, obj))
         return false;
 
+    if (!prop || !IsCacheableProtoChainForIonOrCacheIR(obj, holder))
+        return false;
+
+    Shape* shape = prop.shape();
     return IsCacheableGetPropCallNative(obj, holder, shape) ||
         IsCacheableGetPropCallPropertyOp(obj, holder, shape) ||
         IsCacheableGetPropCallScripted(obj, holder, shape);
@@ -4996,10 +5010,10 @@ NameIC::attachTypeOfNoProperty(JSContext* cx, HandleScript outerScript, IonScrip
 
 static bool
 IsCacheableNameNoProperty(HandleObject envChain, HandleObject obj,
-                          HandleObject holder, HandleShape shape, jsbytecode* pc,
+                          HandleObject holder, Handle<PropertyResult> prop, jsbytecode* pc,
                           NameIC& cache)
 {
-    if (cache.isTypeOf() && !shape) {
+    if (cache.isTypeOf() && !prop) {
         MOZ_ASSERT(!obj);
         MOZ_ASSERT(!holder);
         MOZ_ASSERT(envChain);
@@ -5029,34 +5043,35 @@ NameIC::update(JSContext* cx, HandleScript outerScript, size_t cacheIndex, Handl
 
     RootedObject obj(cx);
     RootedObject holder(cx);
-    RootedShape shape(cx);
-    if (!LookupName(cx, name, envChain, &obj, &holder, &shape))
+    Rooted<PropertyResult> prop(cx);
+    if (!LookupName(cx, name, envChain, &obj, &holder, &prop))
         return false;
 
     // Look first. Don't generate cache entries if the lookup fails.
     if (cache.isTypeOf()) {
-        if (!FetchName<true>(cx, obj, holder, name, shape, vp))
+        if (!FetchName<true>(cx, obj, holder, name, prop, vp))
             return false;
     } else {
-        if (!FetchName<false>(cx, obj, holder, name, shape, vp))
+        if (!FetchName<false>(cx, obj, holder, name, prop, vp))
             return false;
     }
 
     if (cache.canAttachStub()) {
-        if (IsCacheableNameReadSlot(envChain, obj, holder, shape, pc, cache.outputReg())) {
+        if (IsCacheableNameReadSlot(cx, envChain, obj, holder, prop, pc, cache.outputReg())) {
             if (!cache.attachReadSlot(cx, outerScript, ion, envChain, obj,
-                                      holder.as<NativeObject>(), shape))
+                                      holder.as<NativeObject>(), prop))
             {
                 return false;
             }
-        } else if (IsCacheableNameCallGetter(envChain, obj, holder, shape)) {
+        } else if (IsCacheableNameCallGetter(envChain, obj, holder, prop)) {
             void* returnAddr = GetReturnAddressToIonCode(cx);
+            RootedShape shape(cx, prop.shape());
             if (!cache.attachCallGetter(cx, outerScript, ion, envChain, obj, holder, shape,
                                         returnAddr))
             {
                 return false;
             }
-        } else if (IsCacheableNameNoProperty(envChain, obj, holder, shape, pc, cache)) {
+        } else if (IsCacheableNameNoProperty(envChain, obj, holder, prop, pc, cache)) {
             if (!cache.attachTypeOfNoProperty(cx, outerScript, ion, envChain))
                 return false;
         }
diff --git a/js/src/jit/IonCaches.h b/js/src/jit/IonCaches.h
index a7135000e5..914965055b 100644
--- a/js/src/jit/IonCaches.h
+++ b/js/src/jit/IonCaches.h
@@ -806,7 +806,7 @@ class NameIC : public IonCache
 
     MOZ_MUST_USE bool attachReadSlot(JSContext* cx, HandleScript outerScript, IonScript* ion,
                                      HandleObject envChain, HandleObject holderBase,
-                                     HandleNativeObject holder, HandleShape shape);
+                                     HandleNativeObject holder, Handle<PropertyResult> prop);
 
     MOZ_MUST_USE bool attachCallGetter(JSContext* cx, HandleScript outerScript, IonScript* ion,
                                        HandleObject envChain, HandleObject obj,
@@ -839,7 +839,7 @@ IONCACHE_KIND_LIST(CACHE_CASTS)
 #undef OPCODE_CASTS
 
 bool IsCacheableProtoChainForIonOrCacheIR(JSObject* obj, JSObject* holder);
-bool IsCacheableGetPropReadSlotForIonOrCacheIR(JSObject* obj, JSObject* holder, Shape* shape);
+bool IsCacheableGetPropReadSlotForIonOrCacheIR(JSObject* obj, JSObject* holder, PropertyResult prop);
 
 } // namespace jit
 } // namespace js
diff --git a/js/src/jit/SharedIC.cpp b/js/src/jit/SharedIC.cpp
index 1434894193..f8f4433af7 100644
--- a/js/src/jit/SharedIC.cpp
+++ b/js/src/jit/SharedIC.cpp
@@ -2192,12 +2192,12 @@ GetDOMProxyProto(JSObject* obj)
 // existence of the property on the object.
 bool
 EffectlesslyLookupProperty(JSContext* cx, HandleObject obj, HandleId id,
-                           MutableHandleObject holder, MutableHandleShape shape,
+                           MutableHandleObject holder, MutableHandle<PropertyResult> prop,
                            bool* checkDOMProxy,
                            DOMProxyShadowsResult* shadowsResult,
                            bool* domProxyHasGeneration)
 {
-    shape.set(nullptr);
+    prop.setNotFound();
     holder.set(nullptr);
 
     if (checkDOMProxy) {
@@ -2231,11 +2231,11 @@ EffectlesslyLookupProperty(JSContext* cx, HandleObject obj, HandleId id,
             return true;
     }
 
-    if (LookupPropertyPure(cx, checkObj, id, holder.address(), shape.address()))
+    if (LookupPropertyPure(cx, checkObj, id, holder.address(), prop.address()))
         return true;
 
     holder.set(nullptr);
-    shape.set(nullptr);
+    prop.setNotFound();
     return true;
 }
 
@@ -2421,15 +2421,16 @@ TryAttachNativeGetAccessorPropStub(JSContext* cx, SharedStubInfo* info,
     bool isDOMProxy;
     bool domProxyHasGeneration;
     DOMProxyShadowsResult domProxyShadowsResult;
-    RootedShape shape(cx);
+    Rooted<PropertyResult> prop(cx);
     RootedObject holder(cx);
     RootedId id(cx, NameToId(name));
-    if (!EffectlesslyLookupProperty(cx, obj, id, &holder, &shape, &isDOMProxy,
+    if (!EffectlesslyLookupProperty(cx, obj, id, &holder, &prop, &isDOMProxy,
                                     &domProxyShadowsResult, &domProxyHasGeneration))
     {
         return false;
     }
 
+    RootedShape shape(cx, prop.maybeShape());
     ICStub* monitorStub = stub->fallbackMonitorStub()->firstMonitorStub();
 
     bool isScripted = false;
@@ -2492,7 +2493,7 @@ TryAttachNativeGetAccessorPropStub(JSContext* cx, SharedStubInfo* info,
         MOZ_ASSERT(ToWindowIfWindowProxy(obj) == cx->global());
         obj = cx->global();
 
-        if (!EffectlesslyLookupProperty(cx, obj, id, &holder, &shape, &isDOMProxy,
+        if (!EffectlesslyLookupProperty(cx, obj, id, &holder, &prop, &isDOMProxy,
                                         &domProxyShadowsResult, &domProxyHasGeneration))
         {
             return false;
diff --git a/js/src/jit/SharedIC.h b/js/src/jit/SharedIC.h
index 8ad8fd495b..d0038c9378 100644
--- a/js/src/jit/SharedIC.h
+++ b/js/src/jit/SharedIC.h
@@ -2249,7 +2249,7 @@ StripPreliminaryObjectStubs(JSContext* cx, ICFallbackStub* stub);
 
 MOZ_MUST_USE bool
 EffectlesslyLookupProperty(JSContext* cx, HandleObject obj, HandleId name,
-                           MutableHandleObject holder, MutableHandleShape shape,
+                           MutableHandleObject holder, MutableHandle<PropertyResult> prop,
                            bool* checkDOMProxy=nullptr,
                            DOMProxyShadowsResult* shadowsResult=nullptr,
                            bool* domProxyHasGeneration=nullptr);
diff --git a/js/src/jit/VMFunctions.cpp b/js/src/jit/VMFunctions.cpp
index fd41f6fbcb..fbe6977bf9 100644
--- a/js/src/jit/VMFunctions.cpp
+++ b/js/src/jit/VMFunctions.cpp
@@ -583,11 +583,11 @@ GetDynamicName(JSContext* cx, JSObject* envChain, JSString* str, Value* vp)
         return;
     }
 
-    Shape* shape = nullptr;
+    PropertyResult prop;
     JSObject* scope = nullptr;
     JSObject* pobj = nullptr;
-    if (LookupNameNoGC(cx, atom->asPropertyName(), envChain, &scope, &pobj, &shape)) {
-        if (FetchNameNoGC(pobj, shape, MutableHandleValue::fromMarkedLocation(vp)))
+    if (LookupNameNoGC(cx, atom->asPropertyName(), envChain, &scope, &pobj, &prop)) {
+        if (FetchNameNoGC(pobj, prop, MutableHandleValue::fromMarkedLocation(vp)))
             return;
     }
 
diff --git a/js/src/jsapi-tests/testGCExactRooting.cpp b/js/src/jsapi-tests/testGCExactRooting.cpp
index aff65014a9..6d41d374b5 100644
--- a/js/src/jsapi-tests/testGCExactRooting.cpp
+++ b/js/src/jsapi-tests/testGCExactRooting.cpp
@@ -56,19 +56,10 @@ struct MyContainer
 };
 
 namespace js {
-template <>
-struct RootedBase<MyContainer> {
-    HeapPtr<JSObject*>& obj() { return static_cast<Rooted<MyContainer>*>(this)->get().obj; }
-    HeapPtr<JSString*>& str() { return static_cast<Rooted<MyContainer>*>(this)->get().str; }
-};
-template <>
-struct PersistentRootedBase<MyContainer> {
-    HeapPtr<JSObject*>& obj() {
-        return static_cast<PersistentRooted<MyContainer>*>(this)->get().obj;
-    }
-    HeapPtr<JSString*>& str() {
-        return static_cast<PersistentRooted<MyContainer>*>(this)->get().str;
-    }
+template <typename Wrapper>
+struct MutableWrappedPtrOperations<MyContainer, Wrapper> {
+    HeapPtr<JSObject*>& obj() { return static_cast<Wrapper*>(this)->get().obj; }
+    HeapPtr<JSString*>& str() { return static_cast<Wrapper*>(this)->get().str; }
 };
 } // namespace js
 
diff --git a/js/src/jsapi-tests/testGCHeapPostBarriers.cpp b/js/src/jsapi-tests/testGCHeapPostBarriers.cpp
index ccc9869724..2353f9ae46 100644
--- a/js/src/jsapi-tests/testGCHeapPostBarriers.cpp
+++ b/js/src/jsapi-tests/testGCHeapPostBarriers.cpp
@@ -4,6 +4,7 @@
  * 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/. */
 
+#include "mozilla/TypeTraits.h"
 #include "mozilla/UniquePtr.h"
 
 #include "js/RootingAPI.h"
@@ -146,3 +147,110 @@ TestHeapPostBarrierInitFailure()
 }
 
 END_TEST(testGCHeapPostBarriers)
+
+BEGIN_TEST(testUnbarrieredEquality)
+{
+    // Use ArrayBuffers because they have finalizers, which allows using them
+    // in ObjectPtr without awkward conversations about nursery allocatability.
+    JS::RootedObject robj(cx, JS_NewArrayBuffer(cx, 20));
+    JS::RootedObject robj2(cx, JS_NewArrayBuffer(cx, 30));
+    cx->gc.evictNursery(); // Need tenured objects
+
+    // Need some bare pointers to compare against.
+    JSObject* obj = robj;
+    JSObject* obj2 = robj2;
+    const JSObject* constobj = robj;
+    const JSObject* constobj2 = robj2;
+
+    // Make them gray. We will make sure they stay gray. (For most reads, the
+    // barrier will unmark gray.)
+    using namespace js::gc;
+    TenuredCell* cell = &obj->asTenured();
+    TenuredCell* cell2 = &obj2->asTenured();
+    cell->markIfUnmarked(GRAY);
+    cell2->markIfUnmarked(GRAY);
+    MOZ_ASSERT(cell->isMarked(GRAY));
+    MOZ_ASSERT(cell2->isMarked(GRAY));
+
+    {
+        JS::Heap<JSObject*> heap(obj);
+        JS::Heap<JSObject*> heap2(obj2);
+        CHECK(TestWrapper(obj, obj2, heap, heap2));
+        CHECK(TestWrapper(constobj, constobj2, heap, heap2));
+    }
+
+    {
+        JS::TenuredHeap<JSObject*> heap(obj);
+        JS::TenuredHeap<JSObject*> heap2(obj2);
+        CHECK(TestWrapper(obj, obj2, heap, heap2));
+        CHECK(TestWrapper(constobj, constobj2, heap, heap2));
+    }
+
+    {
+        JS::ObjectPtr objptr(obj);
+        JS::ObjectPtr objptr2(obj2);
+        CHECK(TestWrapper(obj, obj2, objptr, objptr2));
+        CHECK(TestWrapper(constobj, constobj2, objptr, objptr2));
+        objptr.finalize(cx);       
+        objptr2.finalize(cx);
+    }
+    // Sanity check that the barriers normally mark things black.
+    {
+        JS::Heap<JSObject*> heap(obj);
+        JS::Heap<JSObject*> heap2(obj2);
+        heap.get();
+        heap2.get();
+        CHECK(cell->isMarked(BLACK));
+        CHECK(cell2->isMarked(BLACK));
+    }
+
+    return true;
+}
+
+template <typename ObjectT, typename WrapperT>
+bool
+TestWrapper(ObjectT obj, ObjectT obj2, WrapperT& wrapper, WrapperT& wrapper2)
+{
+    using namespace js::gc;
+
+    const TenuredCell& cell = obj->asTenured();
+    const TenuredCell& cell2 = obj2->asTenured();
+
+    int x = 0;
+
+    CHECK(cell.isMarked(GRAY));
+    CHECK(cell2.isMarked(GRAY));
+    x += obj == obj2;
+    CHECK(cell.isMarked(GRAY));
+    CHECK(cell2.isMarked(GRAY));
+    x += obj == wrapper2;
+    CHECK(cell.isMarked(GRAY));
+    CHECK(cell2.isMarked(GRAY));
+    x += wrapper == obj2;
+    CHECK(cell.isMarked(GRAY));
+    CHECK(cell2.isMarked(GRAY));
+    x += wrapper == wrapper2;
+    CHECK(cell.isMarked(GRAY));
+    CHECK(cell2.isMarked(GRAY));
+
+    CHECK(x == 0);
+
+    x += obj != obj2;
+    CHECK(cell.isMarked(GRAY));
+    CHECK(cell2.isMarked(GRAY));
+    x += obj != wrapper2;
+    CHECK(cell.isMarked(GRAY));
+    CHECK(cell2.isMarked(GRAY));
+    x += wrapper != obj2;
+    CHECK(cell.isMarked(GRAY));
+    CHECK(cell2.isMarked(GRAY));
+    x += wrapper != wrapper2;
+    CHECK(cell.isMarked(GRAY));
+    CHECK(cell2.isMarked(GRAY));
+
+    CHECK(x == 4);
+
+    return true;
+}
+
+END_TEST(testUnbarrieredEquality)
diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index f4b3c98545..3901a0e63c 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -2947,9 +2947,9 @@ JS_AlreadyHasOwnPropertyById(JSContext* cx, HandleObject obj, HandleId id, bool*
         return js::HasOwnProperty(cx, obj, id, foundp);
 
     RootedNativeObject nativeObj(cx, &obj->as<NativeObject>());
-    RootedShape prop(cx);
+    Rooted<PropertyResult> prop(cx);
     NativeLookupOwnPropertyNoResolve(cx, nativeObj, id, &prop);
-    *foundp = !!prop;
+    *foundp = prop.isFound();
     return true;
 }
 
diff --git a/js/src/jsapi.h b/js/src/jsapi.h
index 1eecdbf749..8e70cc152b 100644
--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -2546,10 +2546,14 @@ struct JS_PUBLIC_API(PropertyDescriptor) {
     void trace(JSTracer* trc);
 };
 
-template <typename Outer>
-class PropertyDescriptorOperations
+} // namespace JS
+
+namespace js {
+
+template <typename Wrapper>
+class WrappedPtrOperations<JS::PropertyDescriptor, Wrapper>
 {
-    const PropertyDescriptor& desc() const { return static_cast<const Outer*>(this)->get(); }
+    const JS::PropertyDescriptor& desc() const { return static_cast<const Wrapper*>(this)->get(); }
 
     bool has(unsigned bit) const {
         MOZ_ASSERT(bit != 0);
@@ -2678,10 +2682,11 @@ class PropertyDescriptorOperations
     }
 };
 
-template <typename Outer>
-class MutablePropertyDescriptorOperations : public PropertyDescriptorOperations<Outer>
+template <typename Wrapper>
+class MutableWrappedPtrOperations<JS::PropertyDescriptor, Wrapper>
+    : public js::WrappedPtrOperations<JS::PropertyDescriptor, Wrapper>
 {
-    PropertyDescriptor& desc() { return static_cast<Outer*>(this)->get(); }
+    JS::PropertyDescriptor& desc() { return static_cast<Wrapper*>(this)->get(); }
 
   public:
     void clear() {
@@ -2692,7 +2697,7 @@ class MutablePropertyDescriptorOperations : public PropertyDescriptorOperations<
         value().setUndefined();
     }
 
-    void initFields(HandleObject obj, HandleValue v, unsigned attrs,
+    void initFields(JS::HandleObject obj, JS::HandleValue v, unsigned attrs,
                     JSGetterOp getterOp, JSSetterOp setterOp) {
         MOZ_ASSERT(getterOp != JS_PropertyStub);
         MOZ_ASSERT(setterOp != JS_StrictPropertyStub);
@@ -2704,7 +2709,7 @@ class MutablePropertyDescriptorOperations : public PropertyDescriptorOperations<
         setSetter(setterOp);
     }
 
-    void assign(PropertyDescriptor& other) {
+    void assign(JS::PropertyDescriptor& other) {
         object().set(other.obj);
         setAttributes(other.attrs);
         setGetter(other.getter);
@@ -2712,7 +2717,7 @@ class MutablePropertyDescriptorOperations : public PropertyDescriptorOperations<
         value().set(other.value);
     }
 
-    void setDataDescriptor(HandleValue v, unsigned attrs) {
+    void setDataDescriptor(JS::HandleValue v, unsigned attrs) {
         MOZ_ASSERT((attrs & ~(JSPROP_ENUMERATE |
                               JSPROP_PERMANENT |
                               JSPROP_READONLY |
@@ -2787,26 +2792,7 @@ class MutablePropertyDescriptorOperations : public PropertyDescriptorOperations<
     }
 };
 
-} /* namespace JS */
-
-namespace js {
-
-template <>
-class RootedBase<JS::PropertyDescriptor>
-  : public JS::MutablePropertyDescriptorOperations<JS::Rooted<JS::PropertyDescriptor>>
-{};
-
-template <>
-class HandleBase<JS::PropertyDescriptor>
-  : public JS::PropertyDescriptorOperations<JS::Handle<JS::PropertyDescriptor>>
-{};
-
-template <>
-class MutableHandleBase<JS::PropertyDescriptor>
-  : public JS::MutablePropertyDescriptorOperations<JS::MutableHandle<JS::PropertyDescriptor>>
-{};
-
-} /* namespace js */
+} // namespace js
 
 namespace JS {
 
diff --git a/js/src/jscompartment.cpp b/js/src/jscompartment.cpp
index ebf2d178fc..5e33f27f7d 100644
--- a/js/src/jscompartment.cpp
+++ b/js/src/jscompartment.cpp
@@ -722,8 +722,9 @@ JSCompartment::sweepAfterMinorGC(JSTracer* trc)
 {
     globalWriteBarriered = 0;
 
-    if (innerViews.needsSweepAfterMinorGC())
-        innerViews.sweepAfterMinorGC();
+    InnerViewTable& table = innerViews.get();
+    if (table.needsSweepAfterMinorGC())
+        table.sweepAfterMinorGC();
 
     crossCompartmentWrappers.sweepAfterMinorGC(trc);
 }
diff --git a/js/src/jsfriendapi.h b/js/src/jsfriendapi.h
index 95f49b35e3..494bcb042a 100644
--- a/js/src/jsfriendapi.h
+++ b/js/src/jsfriendapi.h
@@ -331,7 +331,7 @@ extern JS_FRIEND_DATA(const js::ObjectOps) ProxyObjectOps;
 
 extern JS_FRIEND_API(bool)
 proxy_LookupProperty(JSContext* cx, JS::HandleObject obj, JS::HandleId id, JS::MutableHandleObject objp,
-                    JS::MutableHandle<Shape*> propp);
+                    JS::MutableHandle<JS::PropertyResult> propp);
 extern JS_FRIEND_API(bool)
 proxy_DefineProperty(JSContext* cx, JS::HandleObject obj, JS::HandleId id,
                      JS::Handle<JS::PropertyDescriptor> desc,
diff --git a/js/src/jsobj.cpp b/js/src/jsobj.cpp
index a243f44681..a23ac63366 100644
--- a/js/src/jsobj.cpp
+++ b/js/src/jsobj.cpp
@@ -2116,7 +2116,7 @@ JSObject::constructHook() const
 
 bool
 js::LookupProperty(JSContext* cx, HandleObject obj, js::HandleId id,
-                   MutableHandleObject objp, MutableHandleShape propp)
+                   MutableHandleObject objp, MutableHandle<PropertyResult> propp)
 {
     /* NB: The logic of lookupProperty is implicitly reflected in
      *     BaselineIC.cpp's |EffectlesslyLookupProperty| logic.
@@ -2129,7 +2129,7 @@ js::LookupProperty(JSContext* cx, HandleObject obj, js::HandleId id,
 
 bool
 js::LookupName(JSContext* cx, HandlePropertyName name, HandleObject envChain,
-               MutableHandleObject objp, MutableHandleObject pobjp, MutableHandleShape propp)
+               MutableHandleObject objp, MutableHandleObject pobjp, MutableHandle<PropertyResult> propp)
 {
     RootedId id(cx, NameToId(name));
 
@@ -2144,13 +2144,13 @@ js::LookupName(JSContext* cx, HandlePropertyName name, HandleObject envChain,
 
     objp.set(nullptr);
     pobjp.set(nullptr);
-    propp.set(nullptr);
+    propp.setNotFound();
     return true;
 }
 
 bool
 js::LookupNameNoGC(JSContext* cx, PropertyName* name, JSObject* envChain,
-                   JSObject** objp, JSObject** pobjp, Shape** propp)
+                   JSObject** objp, JSObject** pobjp, PropertyResult* propp)
 {
     AutoAssertNoException nogc(cx);
 
@@ -2177,13 +2177,13 @@ js::LookupNameWithGlobalDefault(JSContext* cx, HandlePropertyName name, HandleOb
     RootedId id(cx, NameToId(name));
 
     RootedObject pobj(cx);
-    RootedShape shape(cx);
+    Rooted<PropertyResult> prop(cx);
 
     RootedObject env(cx, envChain);
     for (; !env->is<GlobalObject>(); env = env->enclosingEnvironment()) {
-        if (!LookupProperty(cx, env, id, &pobj, &shape))
+        if (!LookupProperty(cx, env, id, &pobj, &prop))
             return false;
-        if (shape)
+        if (prop)
             break;
     }
 
@@ -2198,20 +2198,20 @@ js::LookupNameUnqualified(JSContext* cx, HandlePropertyName name, HandleObject e
     RootedId id(cx, NameToId(name));
 
     RootedObject pobj(cx);
-    RootedShape shape(cx);
+    Rooted<PropertyResult> prop(cx);
 
     RootedObject env(cx, envChain);
     for (; !env->isUnqualifiedVarObj(); env = env->enclosingEnvironment()) {
-        if (!LookupProperty(cx, env, id, &pobj, &shape))
+        if (!LookupProperty(cx, env, id, &pobj, &prop))
             return false;
-        if (shape)
+        if (prop)
             break;
     }
 
     // See note above RuntimeLexicalErrorObject.
     if (pobj == env) {
         bool isTDZ = false;
-        if (shape && name != cx->names().dotThis) {
+        if (prop && name != cx->names().dotThis) {
             // Treat Debugger environments specially for TDZ checks, as they
             // look like non-native environments but in fact wrap native
             // environments.
@@ -2222,7 +2222,7 @@ js::LookupNameUnqualified(JSContext* cx, HandlePropertyName name, HandleObject e
                     return false;
                 isTDZ = IsUninitializedLexical(v);
             } else {
-                isTDZ = IsUninitializedLexicalSlot(env, shape);
+                isTDZ = IsUninitializedLexicalSlot(env, prop);
             }
         }
 
@@ -2230,7 +2230,7 @@ js::LookupNameUnqualified(JSContext* cx, HandlePropertyName name, HandleObject e
             env = RuntimeLexicalErrorObject::create(cx, env, JSMSG_UNINITIALIZED_LEXICAL);
             if (!env)
                 return false;
-        } else if (env->is<LexicalEnvironmentObject>() && !shape->writable()) {
+        } else if (env->is<LexicalEnvironmentObject>() && !prop.shape()->writable()) {
             // Assigning to a named lambda callee name is a no-op in sloppy mode.
             Rooted<LexicalEnvironmentObject*> lexicalEnv(cx, &env->as<LexicalEnvironmentObject>());
             if (lexicalEnv->isExtensible() ||
@@ -2262,16 +2262,16 @@ js::HasOwnProperty(JSContext* cx, HandleObject obj, HandleId id, bool* result)
         return true;
     }
 
-    RootedShape shape(cx);
-    if (!NativeLookupOwnProperty<CanGC>(cx, obj.as<NativeObject>(), id, &shape))
+    Rooted<PropertyResult> prop(cx);
+    if (!NativeLookupOwnProperty<CanGC>(cx, obj.as<NativeObject>(), id, &prop))
         return false;
-    *result = (shape != nullptr);
+    *result = prop.isFound();
     return true;
 }
 
 bool
 js::LookupPropertyPure(ExclusiveContext* cx, JSObject* obj, jsid id, JSObject** objp,
-                       Shape** propp)
+                       PropertyResult* propp)
 {
     bool isTypedArrayOutOfRange = false;
     do {
@@ -2292,12 +2292,12 @@ js::LookupPropertyPure(ExclusiveContext* cx, JSObject* obj, jsid id, JSObject**
     } while (obj);
 
     *objp = nullptr;
-    *propp = nullptr;
+    propp->setNotFound();
     return true;
 }
 
 bool
-js::LookupOwnPropertyPure(ExclusiveContext* cx, JSObject* obj, jsid id, Shape** propp,
+js::LookupOwnPropertyPure(ExclusiveContext* cx, JSObject* obj, jsid id, PropertyResult* propp,
                           bool* isTypedArrayOutOfRange /* = nullptr */)
 {
     JS::AutoCheckCannotGC nogc;
@@ -2308,7 +2308,7 @@ js::LookupOwnPropertyPure(ExclusiveContext* cx, JSObject* obj, jsid id, Shape**
         // Search for a native dense element, typed array element, or property.
 
         if (JSID_IS_INT(id) && obj->as<NativeObject>().containsDenseElement(JSID_TO_INT(id))) {
-            MarkDenseOrTypedArrayElementFound<NoGC>(propp);
+            propp->setDenseOrTypedArrayElement();
             return true;
         }
 
@@ -2316,9 +2316,9 @@ js::LookupOwnPropertyPure(ExclusiveContext* cx, JSObject* obj, jsid id, Shape**
             uint64_t index;
             if (IsTypedArrayIndex(id, &index)) {
                 if (index < obj->as<TypedArrayObject>().length()) {
-                    MarkDenseOrTypedArrayElementFound<NoGC>(propp);
+                    propp->setDenseOrTypedArrayElement();
                 } else {
-                    *propp = nullptr;
+                    propp->setNotFound();
                     if (isTypedArrayOutOfRange)
                         *isTypedArrayOutOfRange = true;
                 }
@@ -2327,7 +2327,7 @@ js::LookupOwnPropertyPure(ExclusiveContext* cx, JSObject* obj, jsid id, Shape**
         }
 
         if (Shape* shape = obj->as<NativeObject>().lookupPure(id)) {
-            *propp = shape;
+            propp->setNativeProperty(shape);
             return true;
         }
 
@@ -2337,31 +2337,31 @@ js::LookupOwnPropertyPure(ExclusiveContext* cx, JSObject* obj, jsid id, Shape**
             return false;
     } else if (obj->is<UnboxedPlainObject>()) {
         if (obj->as<UnboxedPlainObject>().containsUnboxedOrExpandoProperty(cx, id)) {
-            MarkNonNativePropertyFound<NoGC>(propp);
+            propp->setNonNativeProperty();
             return true;
         }
     } else if (obj->is<UnboxedArrayObject>()) {
         if (obj->as<UnboxedArrayObject>().containsProperty(cx, id)) {
-            MarkNonNativePropertyFound<NoGC>(propp);
+            propp->setNonNativeProperty();
             return true;
         }
     } else if (obj->is<TypedObject>()) {
         if (obj->as<TypedObject>().typeDescr().hasProperty(cx->names(), id)) {
-            MarkNonNativePropertyFound<NoGC>(propp);
+            propp->setNonNativeProperty();
             return true;
         }
     } else {
         return false;
     }
 
-    *propp = nullptr;
+    propp->setNotFound();
     return true;
 }
 
 static inline bool
-NativeGetPureInline(NativeObject* pobj, jsid id, Shape* shape, Value* vp)
+NativeGetPureInline(NativeObject* pobj, jsid id, PropertyResult prop, Value* vp)
 {
-    if (IsImplicitDenseOrTypedArrayElement(shape)) {
+    if (prop.isDenseOrTypedArrayElement()) {
         // For simplicity we ignore the TypedArray with string index case.
         if (!JSID_IS_INT(id))
             return false;
@@ -2371,6 +2371,7 @@ NativeGetPureInline(NativeObject* pobj, jsid id, Shape* shape, Value* vp)
     }
 
     // Fail if we have a custom getter.
+    Shape* shape = prop.shape();
     if (!shape->hasDefaultGetter())
         return false;
 
@@ -2388,22 +2389,23 @@ bool
 js::GetPropertyPure(ExclusiveContext* cx, JSObject* obj, jsid id, Value* vp)
 {
     JSObject* pobj;
-    Shape* shape;
-    if (!LookupPropertyPure(cx, obj, id, &pobj, &shape))
+    PropertyResult prop;
+    if (!LookupPropertyPure(cx, obj, id, &pobj, &prop))
         return false;
 
-    if (!shape) {
+    if (!prop) {
         vp->setUndefined();
         return true;
     }
 
-    return pobj->isNative() && NativeGetPureInline(&pobj->as<NativeObject>(), id, shape, vp);
+    return pobj->isNative() && NativeGetPureInline(&pobj->as<NativeObject>(), id, prop, vp);
 }
 
 static inline bool
-NativeGetGetterPureInline(Shape* shape, JSFunction** fp)
+NativeGetGetterPureInline(PropertyResult prop, JSFunction** fp)
 {
-    if (!IsImplicitDenseOrTypedArrayElement(shape) && shape->hasGetterObject()) {
+    if (!prop.isDenseOrTypedArrayElement() && prop.shape()->hasGetterObject()) {
+        Shape* shape = prop.shape();
         if (shape->getterObject()->is<JSFunction>()) {
             *fp = &shape->getterObject()->as<JSFunction>();
             return true;
@@ -2420,32 +2422,32 @@ js::GetGetterPure(ExclusiveContext* cx, JSObject* obj, jsid id, JSFunction** fp)
     /* Just like GetPropertyPure, but get getter function, without invoking
      * it. */
     JSObject* pobj;
-    Shape* shape;
-    if (!LookupPropertyPure(cx, obj, id, &pobj, &shape))
+    PropertyResult prop;
+    if (!LookupPropertyPure(cx, obj, id, &pobj, &prop))
         return false;
 
-    if (!shape) {
+    if (!prop) {
         *fp = nullptr;
         return true;
     }
 
-    return pobj->isNative() && NativeGetGetterPureInline(shape, fp);
+    return prop.isNativeProperty() && NativeGetGetterPureInline(prop, fp);
 }
 
 bool
 js::GetOwnGetterPure(ExclusiveContext* cx, JSObject* obj, jsid id, JSFunction** fp)
 {
     JS::AutoCheckCannotGC nogc;
-    Shape* shape;
-    if (!LookupOwnPropertyPure(cx, obj, id, &shape))
+    PropertyResult prop;
+    if (!LookupOwnPropertyPure(cx, obj, id, &prop))
         return false;
 
-    if (!shape) {
+    if (!prop) {
         *fp = nullptr;
         return true;
     }
 
-    return NativeGetGetterPureInline(shape, fp);
+    return prop.isNativeProperty() && NativeGetGetterPureInline(prop, fp); 
 }
 
 bool
@@ -2453,14 +2455,14 @@ js::GetOwnNativeGetterPure(JSContext* cx, JSObject* obj, jsid id, JSNative* nati
 {
     JS::AutoCheckCannotGC nogc;
     *native = nullptr;
-    Shape* shape;
-    if (!LookupOwnPropertyPure(cx, obj, id, &shape))
+    PropertyResult prop;
+    if (!LookupOwnPropertyPure(cx, obj, id, &prop))
         return false;
 
-    if (!shape || IsImplicitDenseOrTypedArrayElement(shape) || !shape->hasGetterObject())
+    if (!prop || prop.isDenseOrTypedArrayElement() || !prop.shape()->hasGetterObject()) 
         return true;
 
-    JSObject* getterObj = shape->getterObject();
+    JSObject* getterObj = prop.shape()->getterObject();
     if (!getterObj->is<JSFunction>())
         return true;
 
@@ -2475,12 +2477,12 @@ js::GetOwnNativeGetterPure(JSContext* cx, JSObject* obj, jsid id, JSNative* nati
 bool
 js::HasOwnDataPropertyPure(JSContext* cx, JSObject* obj, jsid id, bool* result)
 {
-    Shape* shape = nullptr;
-    if (!LookupOwnPropertyPure(cx, obj, id, &shape))
+    PropertyResult prop;
+    if (!LookupOwnPropertyPure(cx, obj, id, &prop))
         return false;
 
-    *result = shape && !IsImplicitDenseOrTypedArrayElement(shape) && shape->hasDefaultGetter() &&
-              shape->hasSlot();
+    *result = prop && !prop.isDenseOrTypedArrayElement() && prop.shape()->hasDefaultGetter() &&
+              prop.shape()->hasSlot();
     return true;
 }
 
diff --git a/js/src/jsobj.h b/js/src/jsobj.h
index ca48f8de7c..5e0cc347f9 100644
--- a/js/src/jsobj.h
+++ b/js/src/jsobj.h
@@ -299,7 +299,6 @@ class JSObject : public js::gc::Cell
 
     static const JS::TraceKind TraceKind = JS::TraceKind::Object;
     static const size_t MaxTagBits = 3;
-    static bool isNullLike(const JSObject* obj) { return uintptr_t(obj) < (1 << MaxTagBits); }
 
     MOZ_ALWAYS_INLINE JS::Zone* zone() const {
         return group_->zone();
@@ -587,21 +586,23 @@ class JSObject : public js::gc::Cell
     void operator=(const JSObject& other) = delete;
 };
 
-template <class U>
+template <typename Wrapper>
+template <typename U>
 MOZ_ALWAYS_INLINE JS::Handle<U*>
-js::RootedBase<JSObject*>::as() const
+js::RootedBase<JSObject*, Wrapper>::as() const
 {
-    const JS::Rooted<JSObject*>& self = *static_cast<const JS::Rooted<JSObject*>*>(this);
-    MOZ_ASSERT(self->is<U>());
+    const Wrapper& self = *static_cast<const Wrapper*>(this);
+    MOZ_ASSERT(self->template is<U>());
     return Handle<U*>::fromMarkedLocation(reinterpret_cast<U* const*>(self.address()));
 }
 
+template <typename Wrapper>
 template <class U>
 MOZ_ALWAYS_INLINE JS::Handle<U*>
-js::HandleBase<JSObject*>::as() const
+js::HandleBase<JSObject*, Wrapper>::as() const
 {
     const JS::Handle<JSObject*>& self = *static_cast<const JS::Handle<JSObject*>*>(this);
-    MOZ_ASSERT(self->is<U>());
+    MOZ_ASSERT(self->template is<U>());
     return Handle<U*>::fromMarkedLocation(reinterpret_cast<U* const*>(self.address()));
 }
 
@@ -633,7 +634,6 @@ struct JSObject_Slots16 : JSObject { void* data[3]; js::Value fslots[16]; };
 /* static */ MOZ_ALWAYS_INLINE void
 JSObject::readBarrier(JSObject* obj)
 {
-    MOZ_ASSERT_IF(obj, !isNullLike(obj));
     if (obj && obj->isTenured())
         obj->asTenured().readBarrier(&obj->asTenured());
 }
@@ -641,7 +641,6 @@ JSObject::readBarrier(JSObject* obj)
 /* static */ MOZ_ALWAYS_INLINE void
 JSObject::writeBarrierPre(JSObject* obj)
 {
-    MOZ_ASSERT_IF(obj, !isNullLike(obj));
     if (obj && obj->isTenured())
         obj->asTenured().writeBarrierPre(&obj->asTenured());
 }
@@ -650,8 +649,6 @@ JSObject::writeBarrierPre(JSObject* obj)
 JSObject::writeBarrierPost(void* cellp, JSObject* prev, JSObject* next)
 {
     MOZ_ASSERT(cellp);
-    MOZ_ASSERT_IF(next, !IsNullTaggedPointer(next));
-    MOZ_ASSERT_IF(prev, !IsNullTaggedPointer(prev));
 
     // If the target needs an entry, add it.
     js::gc::StoreBuffer* buffer;
@@ -997,11 +994,11 @@ GetPropertyDescriptor(JSContext* cx, HandleObject obj, HandleId id,
  */
 extern bool
 LookupProperty(JSContext* cx, HandleObject obj, HandleId id,
-               MutableHandleObject objp, MutableHandleShape propp);
+               MutableHandleObject objp, MutableHandle<PropertyResult> propp);
 
 inline bool
 LookupProperty(JSContext* cx, HandleObject obj, PropertyName* name,
-               MutableHandleObject objp, MutableHandleShape propp)
+               MutableHandleObject objp, MutableHandle<PropertyResult> propp)
 {
     RootedId id(cx, NameToId(name));
     return LookupProperty(cx, obj, id, objp, propp);
@@ -1193,11 +1190,11 @@ ReadPropertyDescriptors(JSContext* cx, HandleObject props, bool checkAccessors,
 /* Read the name using a dynamic lookup on the scopeChain. */
 extern bool
 LookupName(JSContext* cx, HandlePropertyName name, HandleObject scopeChain,
-           MutableHandleObject objp, MutableHandleObject pobjp, MutableHandleShape propp);
+           MutableHandleObject objp, MutableHandleObject pobjp, MutableHandle<PropertyResult> propp);
 
 extern bool
 LookupNameNoGC(JSContext* cx, PropertyName* name, JSObject* scopeChain,
-               JSObject** objp, JSObject** pobjp, Shape** propp);
+               JSObject** objp, JSObject** pobjp, PropertyResult* propp);
 
 /*
  * Like LookupName except returns the global object if 'name' is not found in
@@ -1231,10 +1228,10 @@ FindVariableScope(JSContext* cx, JSFunction** funp);
 
 bool
 LookupPropertyPure(ExclusiveContext* cx, JSObject* obj, jsid id, JSObject** objp,
-                   Shape** propp);
+                   PropertyResult* propp);
 
 bool
-LookupOwnPropertyPure(ExclusiveContext* cx, JSObject* obj, jsid id, Shape** propp,
+LookupOwnPropertyPure(ExclusiveContext* cx, JSObject* obj, jsid id, PropertyResult* propp,
                       bool* isTypedArrayOutOfRange = nullptr);
 
 bool
diff --git a/js/src/jsobjinlines.h b/js/src/jsobjinlines.h
index 8a55cd435c..07eeff655e 100644
--- a/js/src/jsobjinlines.h
+++ b/js/src/jsobjinlines.h
@@ -585,11 +585,11 @@ HasNoToPrimitiveMethodPure(JSObject* obj, JSContext* cx)
 {
     jsid id = SYMBOL_TO_JSID(cx->wellKnownSymbols().toPrimitive);
     JSObject* pobj;
-    Shape* shape;
-    if (!LookupPropertyPure(cx, obj, id, &pobj, &shape))
+    PropertyResult prop;
+    if (!LookupPropertyPure(cx, obj, id, &pobj, &prop))
         return false;
 
-    return !shape;
+    return !prop;
 }
 
 /* ES6 draft rev 28 (2014 Oct 14) 7.1.14 */
diff --git a/js/src/json.cpp b/js/src/json.cpp
index e32994e908..f3cf22dac9 100644
--- a/js/src/json.cpp
+++ b/js/src/json.cpp
@@ -445,9 +445,9 @@ JO(JSContext* cx, HandleObject obj, StringifyContext* scx)
 #ifdef DEBUG
         if (scx->maybeSafely) {
             RootedNativeObject nativeObj(cx, &obj->as<NativeObject>());
-            RootedShape prop(cx);
+            Rooted<PropertyResult> prop(cx);
             NativeLookupOwnPropertyNoResolve(cx, nativeObj, id, &prop);
-            MOZ_ASSERT(prop && prop->isDataDescriptor());
+            MOZ_ASSERT(prop && prop.isNativeProperty() && prop.shape()->isDataDescriptor());
         }
 #endif // DEBUG
         if (!GetProperty(cx, obj, obj, id, &outputValue))
diff --git a/js/src/proxy/Proxy.cpp b/js/src/proxy/Proxy.cpp
index 376bbcdda7..6f91dfb106 100644
--- a/js/src/proxy/Proxy.cpp
+++ b/js/src/proxy/Proxy.cpp
@@ -530,18 +530,18 @@ Proxy::trace(JSTracer* trc, JSObject* proxy)
 
 bool
 js::proxy_LookupProperty(JSContext* cx, HandleObject obj, HandleId id,
-                         MutableHandleObject objp, MutableHandleShape propp)
+                         MutableHandleObject objp, MutableHandle<JS::PropertyResult> propp)
 {
     bool found;
     if (!Proxy::has(cx, obj, id, &found))
         return false;
 
     if (found) {
-        MarkNonNativePropertyFound<CanGC>(propp);
+        propp.setNonNativeProperty();
         objp.set(obj);
     } else {
+        propp.setNotFound();
         objp.set(nullptr);
-        propp.set(nullptr);
     }
     return true;
 }
diff --git a/js/src/vm/ArrayBufferObject.cpp b/js/src/vm/ArrayBufferObject.cpp
index 1de3d3b1ec..5d355ada9d 100644
--- a/js/src/vm/ArrayBufferObject.cpp
+++ b/js/src/vm/ArrayBufferObject.cpp
@@ -352,7 +352,7 @@ ArrayBufferObject::detach(JSContext* cx, Handle<ArrayBufferObject*> buffer,
     // Update all views of the buffer to account for the buffer having been
     // detached, and clear the buffer's data and list of views.
 
-    auto& innerViews = cx->compartment()->innerViews;
+    auto& innerViews = cx->compartment()->innerViews.get();
     if (InnerViewTable::ViewVector* views = innerViews.maybeViewsUnbarriered(buffer)) {
         for (size_t i = 0; i < views->length(); i++)
             NoteViewBufferWasDetached((*views)[i], newContents, cx);
@@ -427,7 +427,7 @@ ArrayBufferObject::changeContents(JSContext* cx, BufferContents newContents,
     setNewData(cx->runtime()->defaultFreeOp(), newContents, ownsState);
 
     // Update all views.
-    auto& innerViews = cx->compartment()->innerViews;
+    auto& innerViews = cx->compartment()->innerViews.get();
     if (InnerViewTable::ViewVector* views = innerViews.maybeViewsUnbarriered(this)) {
         for (size_t i = 0; i < views->length(); i++)
             changeViewContents(cx, (*views)[i], oldDataPointer, newContents);
diff --git a/js/src/vm/ArrayBufferObject.h b/js/src/vm/ArrayBufferObject.h
index e6dbd30961..87dce34ba1 100644
--- a/js/src/vm/ArrayBufferObject.h
+++ b/js/src/vm/ArrayBufferObject.h
@@ -541,7 +541,6 @@ class InnerViewTable
     typedef Vector<ArrayBufferViewObject*, 1, SystemAllocPolicy> ViewVector;
 
     friend class ArrayBufferObject;
-    friend class WeakCacheBase<InnerViewTable>;
 
   private:
     struct MapGCPolicy {
@@ -602,23 +601,15 @@ class InnerViewTable
     size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf);
 };
 
-template <>
-class WeakCacheBase<InnerViewTable>
+template <typename Wrapper>
+class MutableWrappedPtrOperations<InnerViewTable, Wrapper>
+    : public WrappedPtrOperations<InnerViewTable, Wrapper>
 {
     InnerViewTable& table() {
-        return static_cast<JS::WeakCache<InnerViewTable>*>(this)->get();
-    }
-    const InnerViewTable& table() const {
-        return static_cast<const JS::WeakCache<InnerViewTable>*>(this)->get();
+        return static_cast<Wrapper*>(this)->get();
     }
 
   public:
-    InnerViewTable::ViewVector* maybeViewsUnbarriered(ArrayBufferObject* obj) {
-        return table().maybeViewsUnbarriered(obj);
-    }
-    void removeViews(ArrayBufferObject* obj) { table().removeViews(obj); }
-    void sweepAfterMinorGC() { table().sweepAfterMinorGC(); }
-    bool needsSweepAfterMinorGC() const { return table().needsSweepAfterMinorGC(); }
     size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) {
         return table().sizeOfExcludingThis(mallocSizeOf);
     }
diff --git a/js/src/vm/Debugger.cpp b/js/src/vm/Debugger.cpp
index 305555f414..f665dcef9b 100644
--- a/js/src/vm/Debugger.cpp
+++ b/js/src/vm/Debugger.cpp
@@ -10098,12 +10098,14 @@ DebuggerObject::forceLexicalInitializationByName(JSContext* cx, HandleDebuggerOb
 
     RootedObject globalLexical(cx, &referent->lexicalEnvironment());
     RootedObject pobj(cx);
-    RootedShape shape(cx);
-    if (!LookupProperty(cx, globalLexical, id, &pobj, &shape))
+    Rooted<PropertyResult> prop(cx);
+    if (!LookupProperty(cx, globalLexical, id, &pobj, &prop))
         return false;
 
     result = false;
-    if (shape) {
+    if (prop) {
+        MOZ_ASSERT(prop.isNativeProperty());
+        Shape* shape = prop.shape();
         Value v = globalLexical->as<NativeObject>().getSlot(shape->slot());
         if (shape->hasSlot() && v.isMagic() && v.whyMagic() == JS_UNINITIALIZED_LEXICAL) {
             globalLexical->as<NativeObject>().setSlot(shape->slot(), UndefinedValue());
diff --git a/js/src/vm/EnvironmentObject.cpp b/js/src/vm/EnvironmentObject.cpp
index bffa32f6bf..4e74b95ab2 100644
--- a/js/src/vm/EnvironmentObject.cpp
+++ b/js/src/vm/EnvironmentObject.cpp
@@ -518,14 +518,14 @@ ModuleEnvironmentObject::fixEnclosingEnvironmentAfterCompartmentMerge(GlobalObje
 
 /* static */ bool
 ModuleEnvironmentObject::lookupProperty(JSContext* cx, HandleObject obj, HandleId id,
-                                        MutableHandleObject objp, MutableHandleShape propp)
+                                        MutableHandleObject objp, MutableHandle<PropertyResult> propp)
 {
     const IndirectBindingMap& bindings = obj->as<ModuleEnvironmentObject>().importBindings();
     Shape* shape;
     ModuleEnvironmentObject* env;
     if (bindings.lookup(id, &env, &shape)) {
         objp.set(env);
-        propp.set(shape);
+        propp.setNativeProperty(shape);
         return true;
     }
 
@@ -688,13 +688,13 @@ CheckUnscopables(JSContext *cx, HandleObject obj, HandleId id, bool *scopable)
 
 static bool
 with_LookupProperty(JSContext* cx, HandleObject obj, HandleId id,
-                    MutableHandleObject objp, MutableHandleShape propp)
+                    MutableHandleObject objp, MutableHandle<PropertyResult> propp)
 {
     // SpiderMonkey-specific: consider internal '.generator' and '.this' names
     // to be unscopable.
     if (IsUnscopableDotName(cx, id)) {
         objp.set(nullptr);
-        propp.set(nullptr);
+        propp.setNotFound();
         return true;
     }
 
@@ -708,7 +708,7 @@ with_LookupProperty(JSContext* cx, HandleObject obj, HandleId id,
             return false;
         if (!scopable) {
             objp.set(nullptr);
-            propp.set(nullptr);
+            propp.setNotFound();
         }
     }
     return true;
@@ -1104,7 +1104,7 @@ ReportRuntimeLexicalErrorId(JSContext* cx, unsigned errorNumber, HandleId id)
 
 static bool
 lexicalError_LookupProperty(JSContext* cx, HandleObject obj, HandleId id,
-                            MutableHandleObject objp, MutableHandleShape propp)
+                            MutableHandleObject objp, MutableHandle<PropertyResult> propp)
 {
     ReportRuntimeLexicalErrorId(cx, obj->as<RuntimeLexicalErrorObject>().errorNumber(), id);
     return false;
diff --git a/js/src/vm/EnvironmentObject.h b/js/src/vm/EnvironmentObject.h
index 0277e7c65c..752eb5c65c 100644
--- a/js/src/vm/EnvironmentObject.h
+++ b/js/src/vm/EnvironmentObject.h
@@ -407,7 +407,7 @@ class ModuleEnvironmentObject : public EnvironmentObject
 
   private:
     static bool lookupProperty(JSContext* cx, HandleObject obj, HandleId id,
-                               MutableHandleObject objp, MutableHandleShape propp);
+                               MutableHandleObject objp, MutableHandle<PropertyResult> propp);
     static bool hasProperty(JSContext* cx, HandleObject obj, HandleId id, bool* foundp);
     static bool getProperty(JSContext* cx, HandleObject obj, HandleValue receiver, HandleId id,
                             MutableHandleValue vp);
diff --git a/js/src/vm/GeneratorObject.cpp b/js/src/vm/GeneratorObject.cpp
index 018e5a4819..9265a1b628 100644
--- a/js/src/vm/GeneratorObject.cpp
+++ b/js/src/vm/GeneratorObject.cpp
@@ -363,12 +363,14 @@ js::CheckStarGeneratorResumptionValue(JSContext* cx, HandleValue v)
 
     // It should have `value` data property, but the type doesn't matter
     JSObject* ignored;
-    Shape* shape;
-    if (!LookupPropertyPure(cx, obj, NameToId(cx->names().value), &ignored, &shape))
+    PropertyResult prop;
+    if (!LookupPropertyPure(cx, obj, NameToId(cx->names().value), &ignored, &prop))
         return false;
-    if (!shape)
+    if (!prop)
         return false;
-    if (!shape->hasDefaultGetter())
+    if (!prop.isNativeProperty())
+        return false;
+    if (!prop.shape()->hasDefaultGetter())
         return false;
 
     return true;
diff --git a/js/src/vm/Interpreter-inl.h b/js/src/vm/Interpreter-inl.h
index 2e94a2ab22..5c2320d3fb 100644
--- a/js/src/vm/Interpreter-inl.h
+++ b/js/src/vm/Interpreter-inl.h
@@ -78,17 +78,18 @@ IsUninitializedLexical(const Value& val)
 }
 
 static inline bool
-IsUninitializedLexicalSlot(HandleObject obj, HandleShape shape)
+IsUninitializedLexicalSlot(HandleObject obj, Handle<PropertyResult> prop)
 {
-    MOZ_ASSERT(shape);
+    MOZ_ASSERT(prop);
     if (obj->is<WithEnvironmentObject>())
         return false;
-    // We check for IsImplicitDenseOrTypedArrayElement even though the shape
-    // is always a non-indexed property because proxy hooks may return a
-    // "non-native property found" shape, which happens to be encoded in the
-    // same way as the "dense element" shape. See MarkNonNativePropertyFound.
-    if (IsImplicitDenseOrTypedArrayElement(shape) ||
-        !shape->hasSlot() ||
+
+    // Proxy hooks may return a non-native property.
+    if (prop.isNonNativeProperty())
+        return false;
+
+    Shape* shape = prop.shape();
+    if (!shape->hasSlot() ||
         !shape->hasDefaultGetter() ||
         !shape->hasDefaultSetter())
     {
@@ -174,9 +175,9 @@ GetLengthProperty(const Value& lval, MutableHandleValue vp)
 
 template <bool TypeOf> inline bool
 FetchName(JSContext* cx, HandleObject obj, HandleObject obj2, HandlePropertyName name,
-          HandleShape shape, MutableHandleValue vp)
+          Handle<PropertyResult> prop, MutableHandleValue vp)
 {
-    if (!shape) {
+    if (!prop) {
         if (TypeOf) {
             vp.setUndefined();
             return true;
@@ -190,6 +191,7 @@ FetchName(JSContext* cx, HandleObject obj, HandleObject obj2, HandlePropertyName
         if (!GetProperty(cx, obj, obj, id, vp))
             return false;
     } else {
+        RootedShape shape(cx, prop.shape());
         RootedObject normalized(cx, obj);
         if (normalized->is<WithEnvironmentObject>() && !shape->hasDefaultGetter())
             normalized = &normalized->as<WithEnvironmentObject>().object();
@@ -213,9 +215,13 @@ FetchName(JSContext* cx, HandleObject obj, HandleObject obj2, HandlePropertyName
 }
 
 inline bool
-FetchNameNoGC(JSObject* pobj, Shape* shape, MutableHandleValue vp)
+FetchNameNoGC(JSObject* pobj, PropertyResult prop, MutableHandleValue vp)
 {
-    if (!shape || !pobj->isNative() || !shape->isDataDescriptor() || !shape->hasDefaultGetter())
+    if (!prop || !pobj->isNative())
+        return false;
+
+    Shape* shape = prop.shape();
+    if (!shape->isDataDescriptor() || !shape->hasDefaultGetter())
         return false;
 
     vp.set(pobj->as<NativeObject>().getSlot(shape->slot()));
@@ -361,7 +367,7 @@ DefVarOperation(JSContext* cx, HandleObject varobj, HandlePropertyName dn, unsig
     }
 #endif
 
-    RootedShape prop(cx);
+    Rooted<PropertyResult> prop(cx);
     RootedObject obj2(cx);
     if (!LookupProperty(cx, varobj, dn, &obj2, &prop))
         return false;
diff --git a/js/src/vm/Interpreter.cpp b/js/src/vm/Interpreter.cpp
index 56f715e2be..cf58e2d608 100644
--- a/js/src/vm/Interpreter.cpp
+++ b/js/src/vm/Interpreter.cpp
@@ -210,27 +210,27 @@ GetNameOperation(JSContext* cx, InterpreterFrame* fp, jsbytecode* pc, MutableHan
     if (IsGlobalOp(JSOp(*pc)) && !fp->script()->hasNonSyntacticScope())
         obj = &obj->global().lexicalEnvironment();
 
-    Shape* shape = nullptr;
+    PropertyResult prop;
     JSObject* env = nullptr;
     JSObject* pobj = nullptr;
-    if (LookupNameNoGC(cx, name, obj, &env, &pobj, &shape)) {
-        if (FetchNameNoGC(pobj, shape, vp))
+    if (LookupNameNoGC(cx, name, obj, &env, &pobj, &prop)) {
+        if (FetchNameNoGC(pobj, prop, vp))
             return true;
     }
 
     RootedObject objRoot(cx, obj), envRoot(cx), pobjRoot(cx);
     RootedPropertyName nameRoot(cx, name);
-    RootedShape shapeRoot(cx);
+    Rooted<PropertyResult> propRoot(cx);
 
-    if (!LookupName(cx, nameRoot, objRoot, &envRoot, &pobjRoot, &shapeRoot))
+    if (!LookupName(cx, nameRoot, objRoot, &envRoot, &pobjRoot, &propRoot))
         return false;
 
     /* Kludge to allow (typeof foo == "undefined") tests. */
     JSOp op2 = JSOp(pc[JSOP_GETNAME_LENGTH]);
     if (op2 == JSOP_TYPEOF)
-        return FetchName<true>(cx, envRoot, pobjRoot, nameRoot, shapeRoot, vp);
+        return FetchName<true>(cx, envRoot, pobjRoot, nameRoot, propRoot, vp);
 
-    return FetchName<false>(cx, envRoot, pobjRoot, nameRoot, shapeRoot, vp);
+    return FetchName<false>(cx, envRoot, pobjRoot, nameRoot, propRoot, vp);
 }
 
 static inline bool
@@ -238,12 +238,12 @@ GetImportOperation(JSContext* cx, InterpreterFrame* fp, jsbytecode* pc, MutableH
 {
     RootedObject obj(cx, fp->environmentChain()), env(cx), pobj(cx);
     RootedPropertyName name(cx, fp->script()->getName(pc));
-    RootedShape shape(cx);
+    Rooted<PropertyResult> prop(cx);
 
-    MOZ_ALWAYS_TRUE(LookupName(cx, name, obj, &env, &pobj, &shape));
+    MOZ_ALWAYS_TRUE(LookupName(cx, name, obj, &env, &pobj, &prop));
     MOZ_ASSERT(env && env->is<ModuleEnvironmentObject>());
     MOZ_ASSERT(env->as<ModuleEnvironmentObject>().hasImportBinding(name));
-    return FetchName<false>(cx, env, pobj, name, shape, vp);
+    return FetchName<false>(cx, env, pobj, name, prop, vp);
 }
 
 static bool
@@ -1613,11 +1613,7 @@ GetSuperEnvFunction(JSContext* cx, InterpreterRegs& regs)
  */
 
 template<typename T>
-class ReservedRootedBase {
-};
-
-template<typename T>
-class ReservedRooted : public ReservedRootedBase<T>
+class ReservedRooted : public RootedBase<T, ReservedRooted<T>>
 {
     Rooted<T>* savedRoot;
 
@@ -1645,14 +1641,6 @@ class ReservedRooted : public ReservedRootedBase<T>
     DECLARE_POINTER_ASSIGN_OPS(ReservedRooted, T)
 };
 
-template <>
-class ReservedRootedBase<Value> : public ValueOperations<ReservedRooted<Value>>
-{};
-
-template <>
-class ReservedRootedBase<Scope*> : public ScopeCastOperation<ReservedRooted<Scope*>>
-{};
-
 static MOZ_NEVER_INLINE bool
 Interpret(JSContext* cx, RunState& state)
 {
@@ -4400,12 +4388,12 @@ bool
 js::GetEnvironmentName(JSContext* cx, HandleObject envChain, HandlePropertyName name,
                        MutableHandleValue vp)
 {
-    RootedShape shape(cx);
+    Rooted<PropertyResult> prop(cx);
     RootedObject obj(cx), pobj(cx);
-    if (!LookupName(cx, name, envChain, &obj, &pobj, &shape))
+    if (!LookupName(cx, name, envChain, &obj, &pobj, &prop))
         return false;
 
-    if (!shape)
+    if (!prop)
         return ReportIsNotDefined(cx, name);
 
     if (!GetProperty(cx, obj, obj, name, vp))
@@ -4427,12 +4415,12 @@ bool
 js::GetEnvironmentNameForTypeOf(JSContext* cx, HandleObject envChain, HandlePropertyName name,
                                 MutableHandleValue vp)
 {
-    RootedShape shape(cx);
+    Rooted<PropertyResult> prop(cx);
     RootedObject obj(cx), pobj(cx);
-    if (!LookupName(cx, name, envChain, &obj, &pobj, &shape))
+    if (!LookupName(cx, name, envChain, &obj, &pobj, &prop))
         return false;
 
-    if (!shape) {
+    if (!prop) {
         vp.set(UndefinedValue());
         return true;
     }
@@ -4490,9 +4478,9 @@ js::DefFunOperation(JSContext* cx, HandleScript script, HandleObject envChain,
     /* ES5 10.5 (NB: with subsequent errata). */
     RootedPropertyName name(cx, fun->explicitName()->asPropertyName());
 
-    RootedShape shape(cx);
+    Rooted<PropertyResult> prop(cx);
     RootedObject pobj(cx);
-    if (!LookupProperty(cx, parent, name, &pobj, &shape))
+    if (!LookupProperty(cx, parent, name, &pobj, &prop))
         return false;
 
     RootedValue rval(cx, ObjectValue(*fun));
@@ -4506,7 +4494,7 @@ js::DefFunOperation(JSContext* cx, HandleScript script, HandleObject envChain,
                      : JSPROP_ENUMERATE | JSPROP_PERMANENT;
 
     /* Steps 5d, 5f. */
-    if (!shape || pobj != parent) {
+    if (!prop || pobj != parent) {
         if (!DefineProperty(cx, parent, name, rval, nullptr, nullptr, attrs))
             return false;
 
@@ -4524,6 +4512,7 @@ js::DefFunOperation(JSContext* cx, HandleScript script, HandleObject envChain,
      */
     MOZ_ASSERT(parent->isNative() || parent->is<DebugEnvironmentProxy>());
     if (parent->is<GlobalObject>()) {
+        Shape* shape = prop.shape();
         if (shape->configurable()) {
             if (!DefineProperty(cx, parent, name, rval, nullptr, nullptr, attrs))
                 return false;
@@ -4728,8 +4717,8 @@ js::DeleteNameOperation(JSContext* cx, HandlePropertyName name, HandleObject sco
                         MutableHandleValue res)
 {
     RootedObject scope(cx), pobj(cx);
-    RootedShape shape(cx);
-    if (!LookupName(cx, name, scopeObj, &scope, &pobj, &shape))
+    Rooted<PropertyResult> prop(cx);
+    if (!LookupName(cx, name, scopeObj, &scope, &pobj, &prop))
         return false;
 
     if (!scope) {
diff --git a/js/src/vm/JSONParser.h b/js/src/vm/JSONParser.h
index 6f91391db0..70ed86f58e 100644
--- a/js/src/vm/JSONParser.h
+++ b/js/src/vm/JSONParser.h
@@ -255,10 +255,13 @@ class MOZ_STACK_CLASS JSONParser : public JSONParserBase
     void operator=(const JSONParser& other) = delete;
 };
 
-template <typename CharT>
-struct RootedBase<JSONParser<CharT>> {
+template <typename CharT, typename Wrapper>
+class MutableWrappedPtrOperations<JSONParser<CharT>, Wrapper>
+  : public WrappedPtrOperations<JSONParser<CharT>, Wrapper>
+{
+  public:
     bool parse(MutableHandleValue vp) {
-        return static_cast<Rooted<JSONParser<CharT>>*>(this)->get().parse(vp);
+        return static_cast<Wrapper*>(this)->get().parse(vp);
     }
 };
 
diff --git a/js/src/vm/NativeObject-inl.h b/js/src/vm/NativeObject-inl.h
index 2bb70b7d90..004b308f05 100644
--- a/js/src/vm/NativeObject-inl.h
+++ b/js/src/vm/NativeObject-inl.h
@@ -290,7 +290,7 @@ NativeObject::setSlotWithType(ExclusiveContext* cx, Shape* shape,
 inline void
 NativeObject::updateShapeAfterMovingGC()
 {
-    Shape* shape = shape_.unbarrieredGet();
+    Shape* shape = shape_;
     if (IsForwarded(shape))
         shape_.unsafeSet(Forwarded(shape));
 }
@@ -382,8 +382,8 @@ NewNativeObjectWithClassProto(ExclusiveContext* cx, const Class* clasp, HandleOb
  *     *recursedp = false and return true.
  */
 static MOZ_ALWAYS_INLINE bool
-CallResolveOp(JSContext* cx, HandleNativeObject obj, HandleId id, MutableHandleShape propp,
-              bool* recursedp)
+CallResolveOp(JSContext* cx, HandleNativeObject obj, HandleId id,
+              MutableHandle<PropertyResult> propp, bool* recursedp)
 {
     // Avoid recursion on (obj, id) already being resolved on cx.
     AutoResolving resolving(cx, obj, id);
@@ -407,13 +407,18 @@ CallResolveOp(JSContext* cx, HandleNativeObject obj, HandleId id, MutableHandleS
                   obj->getClass()->getMayResolve()(cx->names(), id, obj));
 
     if (JSID_IS_INT(id) && obj->containsDenseElement(JSID_TO_INT(id))) {
-        MarkDenseOrTypedArrayElementFound<CanGC>(propp);
+        propp.setDenseOrTypedArrayElement();
         return true;
     }
 
     MOZ_ASSERT(!obj->is<TypedArrayObject>());
 
-    propp.set(obj->lookup(cx, id));
+    RootedShape shape(cx, obj->lookup(cx, id));
+    if (shape)
+        propp.setNativeProperty(shape);
+    else
+        propp.setNotFound();
+
     return true;
 }
 
@@ -444,12 +449,12 @@ static MOZ_ALWAYS_INLINE bool
 LookupOwnPropertyInline(ExclusiveContext* cx,
                         typename MaybeRooted<NativeObject*, allowGC>::HandleType obj,
                         typename MaybeRooted<jsid, allowGC>::HandleType id,
-                        typename MaybeRooted<Shape*, allowGC>::MutableHandleType propp,
+                        typename MaybeRooted<PropertyResult, allowGC>::MutableHandleType propp,
                         bool* donep)
 {
     // Check for a native dense element.
     if (JSID_IS_INT(id) && obj->containsDenseElement(JSID_TO_INT(id))) {
-        MarkDenseOrTypedArrayElementFound<allowGC>(propp);
+        propp.setDenseOrTypedArrayElement();
         *donep = true;
         return true;
     }
@@ -460,11 +465,10 @@ LookupOwnPropertyInline(ExclusiveContext* cx,
     if (obj->template is<TypedArrayObject>()) {
         uint64_t index;
         if (IsTypedArrayIndex(id, &index)) {
-            if (index < obj->template as<TypedArrayObject>().length()) {
-                MarkDenseOrTypedArrayElementFound<allowGC>(propp);
-            } else {
-                propp.set(nullptr);
-            }
+            if (index < obj->template as<TypedArrayObject>().length())
+                propp.setDenseOrTypedArrayElement();
+            else
+                propp.setNotFound();
             *donep = true;
             return true;
         }
@@ -472,7 +476,7 @@ LookupOwnPropertyInline(ExclusiveContext* cx,
 
     // Check for a native property.
     if (Shape* shape = obj->lookup(cx, id)) {
-        propp.set(shape);
+        propp.setNativeProperty(shape);
         *donep = true;
         return true;
     }
@@ -486,14 +490,14 @@ LookupOwnPropertyInline(ExclusiveContext* cx,
         if (!CallResolveOp(cx->asJSContext(),
                            MaybeRooted<NativeObject*, allowGC>::toHandle(obj),
                            MaybeRooted<jsid, allowGC>::toHandle(id),
-                           MaybeRooted<Shape*, allowGC>::toMutableHandle(propp),
+                           MaybeRooted<PropertyResult, allowGC>::toMutableHandle(propp),
                            &recursed))
         {
             return false;
         }
 
         if (recursed) {
-            propp.set(nullptr);
+            propp.setNotFound();
             *donep = true;
             return true;
         }
@@ -504,7 +508,7 @@ LookupOwnPropertyInline(ExclusiveContext* cx,
         }
     }
 
-    propp.set(nullptr);
+    propp.setNotFound();
     *donep = false;
     return true;
 }
@@ -515,11 +519,11 @@ LookupOwnPropertyInline(ExclusiveContext* cx,
  */
 static inline void
 NativeLookupOwnPropertyNoResolve(ExclusiveContext* cx, HandleNativeObject obj, HandleId id,
-                                 MutableHandleShape result)
+                                 MutableHandle<PropertyResult> result)
 {
     // Check for a native dense element.
     if (JSID_IS_INT(id) && obj->containsDenseElement(JSID_TO_INT(id))) {
-        MarkDenseOrTypedArrayElementFound<CanGC>(result);
+        result.setDenseOrTypedArrayElement();
         return;
     }
 
@@ -528,15 +532,18 @@ NativeLookupOwnPropertyNoResolve(ExclusiveContext* cx, HandleNativeObject obj, H
         uint64_t index;
         if (IsTypedArrayIndex(id, &index)) {
             if (index < obj->as<TypedArrayObject>().length())
-                MarkDenseOrTypedArrayElementFound<CanGC>(result);
+                result.setDenseOrTypedArrayElement();
             else
-                result.set(nullptr);
+                result.setNotFound();
             return;
         }
     }
 
     // Check for a native property.
-    result.set(obj->lookup(cx, id));
+    if (Shape* shape = obj->lookup(cx, id))
+        result.setNativeProperty(shape);
+    else
+        result.setNotFound();
 }
 
 template <AllowGC allowGC>
@@ -545,7 +552,7 @@ LookupPropertyInline(ExclusiveContext* cx,
                      typename MaybeRooted<NativeObject*, allowGC>::HandleType obj,
                      typename MaybeRooted<jsid, allowGC>::HandleType id,
                      typename MaybeRooted<JSObject*, allowGC>::MutableHandleType objp,
-                     typename MaybeRooted<Shape*, allowGC>::MutableHandleType propp)
+                     typename MaybeRooted<PropertyResult, allowGC>::MutableHandleType propp)
 {
     /* NB: The logic of this procedure is implicitly reflected in
      *     BaselineIC.cpp's |EffectlesslyLookupProperty| logic.
@@ -578,14 +585,14 @@ LookupPropertyInline(ExclusiveContext* cx,
                                   MaybeRooted<JSObject*, allowGC>::toHandle(proto),
                                   MaybeRooted<jsid, allowGC>::toHandle(id),
                                   MaybeRooted<JSObject*, allowGC>::toMutableHandle(objp),
-                                  MaybeRooted<Shape*, allowGC>::toMutableHandle(propp));
+                                  MaybeRooted<PropertyResult, allowGC>::toMutableHandle(propp));
         }
 
         current = &proto->template as<NativeObject>();
     }
 
     objp.set(nullptr);
-    propp.set(nullptr);
+    propp.setNotFound();
     return true;
 }
 
diff --git a/js/src/vm/NativeObject.cpp b/js/src/vm/NativeObject.cpp
index 3625d86f54..53f7c0bfac 100644
--- a/js/src/vm/NativeObject.cpp
+++ b/js/src/vm/NativeObject.cpp
@@ -1044,7 +1044,7 @@ bool
 js::NativeLookupOwnProperty(ExclusiveContext* cx,
                             typename MaybeRooted<NativeObject*, allowGC>::HandleType obj,
                             typename MaybeRooted<jsid, allowGC>::HandleType id,
-                            typename MaybeRooted<Shape*, allowGC>::MutableHandleType propp)
+                            typename MaybeRooted<PropertyResult, allowGC>::MutableHandleType propp)
 {
     bool done;
     return LookupOwnPropertyInline<allowGC>(cx, obj, id, propp, &done);
@@ -1052,11 +1052,11 @@ js::NativeLookupOwnProperty(ExclusiveContext* cx,
 
 template bool
 js::NativeLookupOwnProperty<CanGC>(ExclusiveContext* cx, HandleNativeObject obj, HandleId id,
-                                   MutableHandleShape propp);
+                                   MutableHandle<PropertyResult> propp);
 
 template bool
 js::NativeLookupOwnProperty<NoGC>(ExclusiveContext* cx, NativeObject* const& obj, const jsid& id,
-                                  FakeMutableHandle<Shape*> propp);
+                                  FakeMutableHandle<PropertyResult> propp);
 
 /*** [[DefineOwnProperty]] ***********************************************************************/
 
@@ -1279,19 +1279,20 @@ GetExistingProperty(JSContext* cx,
 
 static bool
 GetExistingPropertyValue(ExclusiveContext* cx, HandleNativeObject obj, HandleId id,
-                         HandleShape shape, MutableHandleValue vp)
+                         Handle<PropertyResult> prop, MutableHandleValue vp)
 {
-    if (IsImplicitDenseOrTypedArrayElement(shape)) {
+    if (prop.isDenseOrTypedArrayElement()) {
         vp.set(obj->getDenseOrTypedArrayElement(JSID_TO_INT(id)));
         return true;
     }
     if (!cx->shouldBeJSContext())
         return false;
 
-    MOZ_ASSERT(shape->propid() == id);
-    MOZ_ASSERT(obj->contains(cx, shape));
+    MOZ_ASSERT(prop.shape()->propid() == id);
+    MOZ_ASSERT(obj->contains(cx, prop.shape()));
 
     RootedValue receiver(cx, ObjectValue(*obj));
+    RootedShape shape(cx, prop.shape());
     return GetExistingProperty<CanGC>(cx->asJSContext(), receiver, obj, shape, vp);
 }
 
@@ -1302,7 +1303,7 @@ GetExistingPropertyValue(ExclusiveContext* cx, HandleNativeObject obj, HandleId
  */
 static bool
 DefinePropertyIsRedundant(ExclusiveContext* cx, HandleNativeObject obj, HandleId id,
-                          HandleShape shape, unsigned shapeAttrs,
+                          Handle<PropertyResult> prop, unsigned shapeAttrs,
                           Handle<PropertyDescriptor> desc, bool *redundant)
 {
     *redundant = false;
@@ -1319,16 +1320,16 @@ DefinePropertyIsRedundant(ExclusiveContext* cx, HandleNativeObject obj, HandleId
         if (desc.hasValue()) {
             // Get the current value of the existing property.
             RootedValue currentValue(cx);
-            if (!IsImplicitDenseOrTypedArrayElement(shape) &&
-                shape->hasSlot() &&
-                shape->hasDefaultGetter())
+            if (!prop.isDenseOrTypedArrayElement() &&
+                prop.shape()->hasSlot() &&
+                prop.shape()->hasDefaultGetter())
             {
                 // Inline GetExistingPropertyValue in order to omit a type
                 // correctness assertion that's too strict for this particular
                 // call site. For details, see bug 1125624 comments 13-16.
-                currentValue.set(obj->getSlot(shape->slot()));
+                currentValue.set(obj->getSlot(prop.shape()->slot()));
             } else {
-                if (!GetExistingPropertyValue(cx, obj, id, shape, &currentValue))
+                if (!GetExistingPropertyValue(cx, obj, id, prop, &currentValue))
                     return false;
             }
 
@@ -1339,22 +1340,24 @@ DefinePropertyIsRedundant(ExclusiveContext* cx, HandleNativeObject obj, HandleId
         }
 
         GetterOp existingGetterOp =
-            IsImplicitDenseOrTypedArrayElement(shape) ? nullptr : shape->getter();
+            prop.isDenseOrTypedArrayElement() ? nullptr : prop.shape()->getter();
         if (desc.getter() != existingGetterOp)
             return true;
 
         SetterOp existingSetterOp =
-            IsImplicitDenseOrTypedArrayElement(shape) ? nullptr : shape->setter();
+            prop.isDenseOrTypedArrayElement() ? nullptr : prop.shape()->setter();
         if (desc.setter() != existingSetterOp)
             return true;
     } else {
-        if (desc.hasGetterObject()) {
-            if (!(shapeAttrs & JSPROP_GETTER) || desc.getterObject() != shape->getterObject())
-                return true;
+        if (desc.hasGetterObject() &&
+            (!(shapeAttrs & JSPROP_GETTER) || desc.getterObject() != prop.shape()->getterObject()))
+        {
+            return true;
         }
-        if (desc.hasSetterObject()) {
-            if (!(shapeAttrs & JSPROP_SETTER) || desc.setterObject() != shape->setterObject())
-                return true;
+        if (desc.hasSetterObject() &&
+            (!(shapeAttrs & JSPROP_SETTER) || desc.setterObject() != prop.shape()->setterObject()))
+        {
+            return true;
         }
     }
 
@@ -1421,14 +1424,14 @@ js::NativeDefineProperty(ExclusiveContext* cx, HandleNativeObject obj, HandleId
     }
 
     // 9.1.6.1 OrdinaryDefineOwnProperty steps 1-2.
-    RootedShape shape(cx);
+    Rooted<PropertyResult> prop(cx); 
     if (desc_.attributes() & JSPROP_RESOLVING) {
         // We are being called from a resolve or enumerate hook to reify a
         // lazily-resolved property. To avoid reentering the resolve hook and
         // recursing forever, skip the resolve hook when doing this lookup.
-        NativeLookupOwnPropertyNoResolve(cx, obj, id, &shape);
+        NativeLookupOwnPropertyNoResolve(cx, obj, id, &prop);
     } else {
-        if (!NativeLookupOwnProperty<CanGC>(cx, obj, id, &shape))
+        if (!NativeLookupOwnProperty<CanGC>(cx, obj, id, &prop))
             return false;
     }
 
@@ -1443,7 +1446,7 @@ js::NativeDefineProperty(ExclusiveContext* cx, HandleNativeObject obj, HandleId
     Rooted<PropertyDescriptor> desc(cx, desc_);
 
     // Step 2.
-    if (!shape) {
+    if (!prop) {
         if (!obj->nonProxyIsExtensible())
             return result.fail(JSMSG_CANT_DEFINE_PROP_OBJECT_NOT_EXTENSIBLE);
 
@@ -1455,21 +1458,20 @@ js::NativeDefineProperty(ExclusiveContext* cx, HandleNativeObject obj, HandleId
         return result.succeed();
     }
 
-    MOZ_ASSERT(shape);
-
     // Steps 3-4. (Step 3 is a special case of step 4.) We use shapeAttrs as a
     // stand-in for shape in many places below, since shape might not be a
     // pointer to a real Shape (see IsImplicitDenseOrTypedArrayElement).
-    unsigned shapeAttrs = GetShapeAttributes(obj, shape);
+    unsigned shapeAttrs = GetPropertyAttributes(obj, prop);
     bool redundant;
-    if (!DefinePropertyIsRedundant(cx, obj, id, shape, shapeAttrs, desc, &redundant))
+    if (!DefinePropertyIsRedundant(cx, obj, id, prop, shapeAttrs, desc, &redundant))
         return false;
     if (redundant) {
         // In cases involving JSOP_NEWOBJECT and JSOP_INITPROP, obj can have a
         // type for this property that doesn't match the value in the slot.
         // Update the type here, even though this DefineProperty call is
         // otherwise a no-op. (See bug 1125624 comment 13.)
-        if (!IsImplicitDenseOrTypedArrayElement(shape) && desc.hasValue()) {
+        if (!prop.isDenseOrTypedArrayElement() && desc.hasValue()) {
+            RootedShape shape(cx, prop.shape());
             if (!UpdateShapeTypeAndValue(cx, obj, shape, desc.value()))
                 return false;
         }
@@ -1512,24 +1514,24 @@ js::NativeDefineProperty(ExclusiveContext* cx, HandleNativeObject obj, HandleId
         MOZ_ASSERT(!desc.hasSetterObject());
         if (IsDataDescriptor(shapeAttrs)) {
             RootedValue currentValue(cx);
-            if (!GetExistingPropertyValue(cx, obj, id, shape, &currentValue))
+            if (!GetExistingPropertyValue(cx, obj, id, prop, &currentValue))
                 return false;
             desc.setValue(currentValue);
             desc.setWritable(IsWritable(shapeAttrs));
         } else {
-            desc.setGetterObject(shape->getterObject());
-            desc.setSetterObject(shape->setterObject());
+            desc.setGetterObject(prop.shape()->getterObject());
+            desc.setSetterObject(prop.shape()->setterObject());
         }
     } else if (desc.isDataDescriptor() != IsDataDescriptor(shapeAttrs)) {
         // Step 7.
         if (!IsConfigurable(shapeAttrs) && !skipRedefineChecks)
             return result.fail(JSMSG_CANT_REDEFINE_PROP);
 
-        if (IsImplicitDenseOrTypedArrayElement(shape)) {
+        if (prop.isDenseOrTypedArrayElement()) {
             MOZ_ASSERT(!obj->is<TypedArrayObject>());
             if (!NativeObject::sparsifyDenseElement(cx, obj, JSID_TO_INT(id)))
                 return false;
-            shape = obj->lookup(cx, id);
+            prop.setNativeProperty(obj->lookup(cx, id));
         }
 
         // Fill in desc fields with default values (steps 7.b.i and 7.c.i).
@@ -1541,15 +1543,15 @@ js::NativeDefineProperty(ExclusiveContext* cx, HandleNativeObject obj, HandleId
             return result.fail(JSMSG_CANT_REDEFINE_PROP);
 
         if (frozen || !desc.hasValue()) {
-            if (IsImplicitDenseOrTypedArrayElement(shape)) {
+            if (prop.isDenseOrTypedArrayElement()) {
                 MOZ_ASSERT(!obj->is<TypedArrayObject>());
                 if (!NativeObject::sparsifyDenseElement(cx, obj, JSID_TO_INT(id)))
                     return false;
-                shape = obj->lookup(cx, id);
+                prop.setNativeProperty(obj->lookup(cx, id));
             }
 
             RootedValue currentValue(cx);
-            if (!GetExistingPropertyValue(cx, obj, id, shape, &currentValue))
+            if (!GetExistingPropertyValue(cx, obj, id, prop, &currentValue))
                 return false;
 
             if (!desc.hasValue()) {
@@ -1571,32 +1573,32 @@ js::NativeDefineProperty(ExclusiveContext* cx, HandleNativeObject obj, HandleId
             desc.setWritable(IsWritable(shapeAttrs));
     } else {
         // Step 9.
-        MOZ_ASSERT(shape->isAccessorDescriptor());
+        MOZ_ASSERT(prop.shape()->isAccessorDescriptor());
         MOZ_ASSERT(desc.isAccessorDescriptor());
 
         // The spec says to use SameValue, but since the values in
         // question are objects, we can just compare pointers.
         if (desc.hasSetterObject()) {
             if (!IsConfigurable(shapeAttrs) &&
-                desc.setterObject() != shape->setterObject() &&
+                desc.setterObject() != prop.shape()->setterObject() &&
                 !skipRedefineChecks)
             {
                 return result.fail(JSMSG_CANT_REDEFINE_PROP);
             }
         } else {
             // Fill in desc.[[Set]] from shape.
-            desc.setSetterObject(shape->setterObject());
+            desc.setSetterObject(prop.shape()->setterObject());
         }
         if (desc.hasGetterObject()) {
             if (!IsConfigurable(shapeAttrs) &&
-                desc.getterObject() != shape->getterObject() &&
+                desc.getterObject() != prop.shape()->getterObject() &&
                 !skipRedefineChecks)
             {
                 return result.fail(JSMSG_CANT_REDEFINE_PROP);
             }
         } else {
             // Fill in desc.[[Get]] from shape.
-            desc.setGetterObject(shape->getterObject());
+            desc.setGetterObject(prop.shape()->getterObject());
         }
     }
 
@@ -1681,18 +1683,18 @@ bool
 js::NativeHasProperty(JSContext* cx, HandleNativeObject obj, HandleId id, bool* foundp)
 {
     RootedNativeObject pobj(cx, obj);
-    RootedShape shape(cx);
+    Rooted<PropertyResult> prop(cx);
 
     // This loop isn't explicit in the spec algorithm. See the comment on step
     // 7.a. below.
     for (;;) {
         // Steps 2-3. ('done' is a SpiderMonkey-specific thing, used below.)
         bool done;
-        if (!LookupOwnPropertyInline<CanGC>(cx, pobj, id, &shape, &done))
+        if (!LookupOwnPropertyInline<CanGC>(cx, pobj, id, &prop, &done))
             return false;
 
         // Step 4.
-        if (shape) {
+        if (prop) {
             *foundp = true;
             return true;
         }
@@ -1733,15 +1735,15 @@ bool
 js::NativeGetOwnPropertyDescriptor(JSContext* cx, HandleNativeObject obj, HandleId id,
                                    MutableHandle<PropertyDescriptor> desc)
 {
-    RootedShape shape(cx);
-    if (!NativeLookupOwnProperty<CanGC>(cx, obj, id, &shape))
+    Rooted<PropertyResult> prop(cx);
+    if (!NativeLookupOwnProperty<CanGC>(cx, obj, id, &prop))
         return false;
-    if (!shape) {
+    if (!prop) {
         desc.object().set(nullptr);
         return true;
     }
 
-    desc.setAttributes(GetShapeAttributes(obj, shape));
+    desc.setAttributes(GetPropertyAttributes(obj, prop));
     if (desc.isAccessorDescriptor()) {
         MOZ_ASSERT(desc.isShared());
 
@@ -1754,13 +1756,13 @@ js::NativeGetOwnPropertyDescriptor(JSContext* cx, HandleNativeObject obj, Handle
         // than return true with desc incomplete, we fill out the missing
         // getter or setter with a null, following CompletePropertyDescriptor.
         if (desc.hasGetterObject()) {
-            desc.setGetterObject(shape->getterObject());
+            desc.setGetterObject(prop.shape()->getterObject());
         } else {
             desc.setGetterObject(nullptr);
             desc.attributesRef() |= JSPROP_GETTER;
         }
         if (desc.hasSetterObject()) {
-            desc.setSetterObject(shape->setterObject());
+            desc.setSetterObject(prop.shape()->setterObject());
         } else {
             desc.setSetterObject(nullptr);
             desc.attributesRef() |= JSPROP_SETTER;
@@ -1776,9 +1778,10 @@ js::NativeGetOwnPropertyDescriptor(JSContext* cx, HandleNativeObject obj, Handle
         desc.setSetter(nullptr);
         desc.attributesRef() &= ~JSPROP_SHARED;
 
-        if (IsImplicitDenseOrTypedArrayElement(shape)) {
+        if (prop.isDenseOrTypedArrayElement()) {
             desc.value().set(obj->getDenseOrTypedArrayElement(JSID_TO_INT(id)));
         } else {
+            RootedShape shape(cx, prop.shape());
             if (!NativeGetExistingProperty(cx, obj, obj, shape, desc.value()))
                 return false;
         }
@@ -2058,23 +2061,25 @@ NativeGetPropertyInline(JSContext* cx,
                         typename MaybeRooted<Value, allowGC>::MutableHandleType vp)
 {
     typename MaybeRooted<NativeObject*, allowGC>::RootType pobj(cx, obj);
-    typename MaybeRooted<Shape*, allowGC>::RootType shape(cx);
+    typename MaybeRooted<PropertyResult, allowGC>::RootType prop(cx);
 
     // This loop isn't explicit in the spec algorithm. See the comment on step
     // 4.d below.
     for (;;) {
         // Steps 2-3. ('done' is a SpiderMonkey-specific thing, used below.)
         bool done;
-        if (!LookupOwnPropertyInline<allowGC>(cx, pobj, id, &shape, &done))
+        if (!LookupOwnPropertyInline<allowGC>(cx, pobj, id, &prop, &done))
             return false;
 
-        if (shape) {
+        if (prop) {
             // Steps 5-8. Special case for dense elements because
             // GetExistingProperty doesn't support those.
-            if (IsImplicitDenseOrTypedArrayElement(shape)) {
+            if (prop.isDenseOrTypedArrayElement()) {
                 vp.set(pobj->getDenseOrTypedArrayElement(JSID_TO_INT(id)));
                 return true;
             }
+
+            typename MaybeRooted<Shape*, allowGC>::RootType shape(cx, prop.shape());
             return GetExistingProperty<allowGC>(cx, receiver, pobj, shape, vp);
         }
 
@@ -2366,11 +2371,11 @@ SetDenseOrTypedArrayElement(JSContext* cx, HandleNativeObject obj, uint32_t inde
  */
 static bool
 SetExistingProperty(JSContext* cx, HandleNativeObject obj, HandleId id, HandleValue v,
-                    HandleValue receiver, HandleNativeObject pobj, HandleShape shape,
+                    HandleValue receiver, HandleNativeObject pobj, Handle<PropertyResult> prop,
                     ObjectOpResult& result)
 {
     // Step 5 for dense elements.
-    if (IsImplicitDenseOrTypedArrayElement(shape)) {
+    if (prop.isDenseOrTypedArrayElement()) {
         // Step 5.a.
         if (pobj->getElementsHeader()->isFrozen())
             return result.fail(JSMSG_READ_ONLY);
@@ -2384,6 +2389,7 @@ SetExistingProperty(JSContext* cx, HandleNativeObject obj, HandleId id, HandleVa
     }
 
     // Step 5 for all other properties.
+    RootedShape shape(cx, prop.shape());
     if (shape->isDataDescriptor()) {
         // Step 5.a.
         if (!shape->writable())
@@ -2441,7 +2447,7 @@ js::NativeSetProperty(JSContext* cx, HandleNativeObject obj, HandleId id, Handle
     // Step numbers below reference ES6 rev 27 9.1.9, the [[Set]] internal
     // method for ordinary objects. We substitute our own names for these names
     // used in the spec: O -> pobj, P -> id, ownDesc -> shape.
-    RootedShape shape(cx);
+    Rooted<PropertyResult> prop(cx);
     RootedNativeObject pobj(cx, obj);
 
     // This loop isn't explicit in the spec algorithm. See the comment on step
@@ -2450,12 +2456,12 @@ js::NativeSetProperty(JSContext* cx, HandleNativeObject obj, HandleId id, Handle
     for (;;) {
         // Steps 2-3. ('done' is a SpiderMonkey-specific thing, used below.)
         bool done;
-        if (!LookupOwnPropertyInline<CanGC>(cx, pobj, id, &shape, &done))
+        if (!LookupOwnPropertyInline<CanGC>(cx, pobj, id, &prop, &done))
             return false;
 
-        if (shape) {
+        if (prop) {
             // Steps 5-6.
-            return SetExistingProperty(cx, obj, id, v, receiver, pobj, shape, result);
+            return SetExistingProperty(cx, obj, id, v, receiver, pobj, prop, result);
         }
 
         // Steps 4.a-b. The check for 'done' on this next line is tricky.
@@ -2513,12 +2519,12 @@ js::NativeDeleteProperty(JSContext* cx, HandleNativeObject obj, HandleId id,
                          ObjectOpResult& result)
 {
     // Steps 2-3.
-    RootedShape shape(cx);
-    if (!NativeLookupOwnProperty<CanGC>(cx, obj, id, &shape))
+    Rooted<PropertyResult> prop(cx);
+    if (!NativeLookupOwnProperty<CanGC>(cx, obj, id, &prop))
         return false;
 
     // Step 4.
-    if (!shape) {
+    if (!prop) {
         // If no property call the class's delProperty hook, passing succeeded
         // as the result parameter. This always succeeds when there is no hook.
         return CallJSDeletePropertyOp(cx, obj->getClass()->getDelProperty(), obj, id, result);
@@ -2527,7 +2533,7 @@ js::NativeDeleteProperty(JSContext* cx, HandleNativeObject obj, HandleId id,
     cx->runtime()->gc.poke();
 
     // Step 6. Non-configurable property.
-    if (GetShapeAttributes(obj, shape) & JSPROP_PERMANENT)
+    if (GetPropertyAttributes(obj, prop) & JSPROP_PERMANENT)
         return result.failCantDelete();
 
     if (!CallJSDeletePropertyOp(cx, obj->getClass()->getDelProperty(), obj, id, result))
@@ -2536,7 +2542,7 @@ js::NativeDeleteProperty(JSContext* cx, HandleNativeObject obj, HandleId id,
         return true;
 
     // Step 5.
-    if (IsImplicitDenseOrTypedArrayElement(shape)) {
+    if (prop.isDenseOrTypedArrayElement()) {
         // Typed array elements are non-configurable.
         MOZ_ASSERT(!obj->is<TypedArrayObject>());
 
diff --git a/js/src/vm/NativeObject.h b/js/src/vm/NativeObject.h
index 657fc8d57c..abc84c9fd1 100644
--- a/js/src/vm/NativeObject.h
+++ b/js/src/vm/NativeObject.h
@@ -1459,7 +1459,7 @@ extern bool
 NativeLookupOwnProperty(ExclusiveContext* cx,
                         typename MaybeRooted<NativeObject*, allowGC>::HandleType obj,
                         typename MaybeRooted<jsid, allowGC>::HandleType id,
-                        typename MaybeRooted<Shape*, allowGC>::MutableHandleType propp);
+                        typename MaybeRooted<PropertyResult, allowGC>::MutableHandleType propp);
 
 /*
  * Get a property from `receiver`, after having already done a lookup and found
diff --git a/js/src/vm/ObjectGroup.cpp b/js/src/vm/ObjectGroup.cpp
index f2a3305cfd..741531f015 100644
--- a/js/src/vm/ObjectGroup.cpp
+++ b/js/src/vm/ObjectGroup.cpp
@@ -421,7 +421,7 @@ struct ObjectGroupCompartment::NewEntry
     }
 
     static inline bool match(const ObjectGroupCompartment::NewEntry& key, const Lookup& lookup) {
-        TaggedProto proto = key.group.unbarrieredGet()->proto().unbarrieredGet();
+        TaggedProto proto = key.group.unbarrieredGet()->proto();
         JSObject* assoc = key.associated;
         MOZ_ASSERT(proto.hasUniqueId());
         MOZ_ASSERT_IF(assoc, assoc->zone()->hasUniqueId(assoc));
diff --git a/js/src/vm/SavedStacks.h b/js/src/vm/SavedStacks.h
index c6bda2831b..3ea6c40874 100644
--- a/js/src/vm/SavedStacks.h
+++ b/js/src/vm/SavedStacks.h
@@ -265,24 +265,6 @@ class SavedStacks {
         uint32_t column;
     };
 
-    template <typename Outer>
-    struct LocationValueOperations {
-        JSAtom* source() const { return loc().source; }
-        size_t line() const { return loc().line; }
-        uint32_t column() const { return loc().column; }
-      private:
-        const LocationValue& loc() const { return static_cast<const Outer*>(this)->get(); }
-    };
-
-    template <typename Outer>
-    struct MutableLocationValueOperations : public LocationValueOperations<Outer> {
-        void setSource(JSAtom* v) { loc().source = v; }
-        void setLine(size_t v) { loc().line = v; }
-        void setColumn(uint32_t v) { loc().column = v; }
-      private:
-        LocationValue& loc() { return static_cast<Outer*>(this)->get(); }
-    };
-
   private:
     struct PCLocationHasher : public DefaultHasher<PCKey> {
         using ScriptPtrHasher = DefaultHasher<JSScript*>;
@@ -313,15 +295,32 @@ class SavedStacks {
                                   MutableHandle<LocationValue> locationp);
 };
 
-template <>
-class RootedBase<SavedStacks::LocationValue>
-  : public SavedStacks::MutableLocationValueOperations<JS::Rooted<SavedStacks::LocationValue>>
-{};
+template <typename Wrapper>
+struct WrappedPtrOperations<SavedStacks::LocationValue, Wrapper>
+{
+    JSAtom* source() const { return loc().source; }
+    size_t line() const { return loc().line; }
+    uint32_t column() const { return loc().column; }
 
-template <>
-class MutableHandleBase<SavedStacks::LocationValue>
-  : public SavedStacks::MutableLocationValueOperations<JS::MutableHandle<SavedStacks::LocationValue>>
-{};
+  private:
+    const SavedStacks::LocationValue& loc() const {
+        return static_cast<const Wrapper*>(this)->get();
+    }
+};
+
+template <typename Wrapper>
+struct MutableWrappedPtrOperations<SavedStacks::LocationValue, Wrapper>
+    : public WrappedPtrOperations<SavedStacks::LocationValue, Wrapper>
+{
+    void setSource(JSAtom* v) { loc().source = v; }
+    void setLine(size_t v) { loc().line = v; }
+    void setColumn(uint32_t v) { loc().column = v; }
+
+  private:
+    SavedStacks::LocationValue& loc() {
+        return static_cast<Wrapper*>(this)->get();
+    }
+};
 
 UTF8CharsZ
 BuildUTF8StackString(JSContext* cx, HandleObject stack);
diff --git a/js/src/vm/Scope.h b/js/src/vm/Scope.h
index 4f0edcc133..fc1419bb89 100644
--- a/js/src/vm/Scope.h
+++ b/js/src/vm/Scope.h
@@ -22,6 +22,7 @@
 namespace js {
 
 class ModuleObject;
+class Scope;
 
 enum class BindingKind : uint8_t
 {
@@ -223,6 +224,21 @@ class BindingLocation
     }
 };
 
+//
+// Allow using is<T> and as<T> on Rooted<Scope*> and Handle<Scope*>.
+//
+template <typename Wrapper>
+class WrappedPtrOperations<Scope*, Wrapper>
+{
+  public:
+    template <class U>
+    JS::Handle<U*> as() const {
+        const Wrapper& self = *static_cast<const Wrapper*>(this);
+        MOZ_ASSERT_IF(self, self->template is<U>());
+        return Handle<U*>::fromMarkedLocation(reinterpret_cast<U* const*>(self.address()));
+    }
+};
+
 //
 // The base class of all Scopes.
 //
@@ -1338,10 +1354,10 @@ class MOZ_STACK_CLASS ScopeIter
 // Specializations of Rooted containers for the iterators.
 //
 
-template <typename Outer>
-class BindingIterOperations
+template <typename Wrapper>
+class WrappedPtrOperations<BindingIter, Wrapper>
 {
-    const BindingIter& iter() const { return static_cast<const Outer*>(this)->get(); }
+    const BindingIter& iter() const { return static_cast<const Wrapper*>(this)->get(); }
 
   public:
     bool done() const { return iter().done(); }
@@ -1361,19 +1377,20 @@ class BindingIterOperations
     uint32_t nextEnvironmentSlot() const { return iter().nextEnvironmentSlot(); }
 };
 
-template <typename Outer>
-class MutableBindingIterOperations : public BindingIterOperations<Outer>
+template <typename Wrapper>
+class MutableWrappedPtrOperations<BindingIter, Wrapper>
+  : public WrappedPtrOperations<BindingIter, Wrapper>
 {
-    BindingIter& iter() { return static_cast<Outer*>(this)->get(); }
+    BindingIter& iter() { return static_cast<Wrapper*>(this)->get(); }
 
   public:
     void operator++(int) { iter().operator++(1); }
 };
 
-template <typename Outer>
-class ScopeIterOperations
+template <typename Wrapper>
+class WrappedPtrOperations<ScopeIter, Wrapper>
 {
-    const ScopeIter& iter() const { return static_cast<const Outer*>(this)->get(); }
+    const ScopeIter& iter() const { return static_cast<const Wrapper*>(this)->get(); }
 
   public:
     bool done() const { return iter().done(); }
@@ -1384,69 +1401,16 @@ class ScopeIterOperations
     bool hasSyntacticEnvironment() const { return iter().hasSyntacticEnvironment(); }
 };
 
-template <typename Outer>
-class MutableScopeIterOperations : public ScopeIterOperations<Outer>
+template <typename Wrapper>
+class MutableWrappedPtrOperations<ScopeIter, Wrapper>
+  : public WrappedPtrOperations<ScopeIter, Wrapper>
 {
-    ScopeIter& iter() { return static_cast<Outer*>(this)->get(); }
+    ScopeIter& iter() { return static_cast<Wrapper*>(this)->get(); }
 
   public:
     void operator++(int) { iter().operator++(1); }
 };
 
-#define SPECIALIZE_ROOTING_CONTAINERS(Iter, BaseIter)                    \
-    template <>                                                          \
-    class RootedBase<Iter>                                               \
-      : public Mutable##BaseIter##Operations<JS::Rooted<Iter>>           \
-    { };                                                                 \
-                                                                         \
-    template <>                                                          \
-    class MutableHandleBase<Iter>                                        \
-      : public Mutable##BaseIter##Operations<JS::MutableHandle<Iter>>    \
-    { };                                                                 \
-                                                                         \
-    template <>                                                          \
-    class HandleBase<Iter>                                               \
-      : public BaseIter##Operations<JS::Handle<Iter>>                    \
-    { };                                                                 \
-                                                                         \
-    template <>                                                          \
-    class PersistentRootedBase<Iter>                                     \
-      : public Mutable##BaseIter##Operations<JS::PersistentRooted<Iter>> \
-    { }
-
-SPECIALIZE_ROOTING_CONTAINERS(BindingIter, BindingIter);
-SPECIALIZE_ROOTING_CONTAINERS(PositionalFormalParameterIter, BindingIter);
-SPECIALIZE_ROOTING_CONTAINERS(ScopeIter, ScopeIter);
-
-#undef SPECIALIZE_ROOTING_CONTAINERS
-
-//
-// Allow using is<T> and as<T> on Rooted<Scope*> and Handle<Scope*>.
-//
-
-template <typename Outer>
-struct ScopeCastOperation
-{
-    template <class U>
-    JS::Handle<U*> as() const {
-        const Outer& self = *static_cast<const Outer*>(this);
-        MOZ_ASSERT_IF(self, self->template is<U>());
-        return Handle<U*>::fromMarkedLocation(reinterpret_cast<U* const*>(self.address()));
-    }
-};
-
-template <>
-class RootedBase<Scope*> : public ScopeCastOperation<JS::Rooted<Scope*>>
-{ };
-
-template <>
-class HandleBase<Scope*> : public ScopeCastOperation<JS::Handle<Scope*>>
-{ };
-
-template <>
-class MutableHandleBase<Scope*> : public ScopeCastOperation<JS::MutableHandle<Scope*>>
-{ };
-
 } // namespace js
 
 namespace JS {
diff --git a/js/src/vm/Shape-inl.h b/js/src/vm/Shape-inl.h
index 32754740a5..7b7561220e 100644
--- a/js/src/vm/Shape-inl.h
+++ b/js/src/vm/Shape-inl.h
@@ -123,7 +123,7 @@ Shape::new_(ExclusiveContext* cx, Handle<StackShape> other, uint32_t nfixed)
 inline void
 Shape::updateBaseShapeAfterMovingGC()
 {
-    BaseShape* base = base_.unbarrieredGet();
+    BaseShape* base = base_;
     if (IsForwarded(base))
         base_.unsafeSet(Forwarded(base));
 }
@@ -191,17 +191,17 @@ AutoRooterGetterSetter::AutoRooterGetterSetter(ExclusiveContext* cx, uint8_t att
 }
 
 static inline uint8_t
-GetShapeAttributes(JSObject* obj, Shape* shape)
+GetPropertyAttributes(JSObject* obj, PropertyResult prop)
 {
     MOZ_ASSERT(obj->isNative());
 
-    if (IsImplicitDenseOrTypedArrayElement(shape)) {
+    if (prop.isDenseOrTypedArrayElement()) {
         if (obj->is<TypedArrayObject>())
             return JSPROP_ENUMERATE | JSPROP_PERMANENT;
         return obj->as<NativeObject>().getElementsHeader()->elementAttributes();
     }
 
-    return shape->attributes();
+    return prop.shape()->attributes();
 }
 
 } /* namespace js */
diff --git a/js/src/vm/Shape.cpp b/js/src/vm/Shape.cpp
index 7cdf382ed6..c71cef5a7e 100644
--- a/js/src/vm/Shape.cpp
+++ b/js/src/vm/Shape.cpp
@@ -1771,3 +1771,10 @@ JS::ubi::Concrete<js::BaseShape>::size(mozilla::MallocSizeOf mallocSizeOf) const
 {
     return js::gc::Arena::thingSize(get().asTenured().getAllocKind());
 }
+
+void
+PropertyResult::trace(JSTracer* trc)
+{
+    if (isNativeProperty())
+        TraceRoot(trc, &shape_, "PropertyResult::shape_");
+}
diff --git a/js/src/vm/Shape.h b/js/src/vm/Shape.h
index 52b9197da6..bb813997f0 100644
--- a/js/src/vm/Shape.h
+++ b/js/src/vm/Shape.h
@@ -1264,9 +1264,10 @@ struct InitialShapeEntry
 
     bool needsSweep() {
         Shape* ushape = shape.unbarrieredGet();
-        JSObject* protoObj = proto.proto().raw();
+        TaggedProto uproto = proto.proto().unbarrieredGet();
+        JSObject* protoObj = uproto.raw();
         return (gc::IsAboutToBeFinalizedUnbarriered(&ushape) ||
-                (proto.proto().isObject() && gc::IsAboutToBeFinalizedUnbarriered(&protoObj)));
+                (uproto.isObject() && gc::IsAboutToBeFinalizedUnbarriered(&protoObj)));
     }
 };
 
@@ -1356,9 +1357,10 @@ struct StackShape
     void trace(JSTracer* trc);
 };
 
-template <typename Outer>
-class StackShapeOperations {
-    const StackShape& ss() const { return static_cast<const Outer*>(this)->get(); }
+template <typename Wrapper>
+class WrappedPtrOperations<StackShape, Wrapper>
+{
+    const StackShape& ss() const { return static_cast<const Wrapper*>(this)->get(); }
 
   public:
     bool hasSlot() const { return ss().hasSlot(); }
@@ -1370,9 +1372,11 @@ class StackShapeOperations {
     uint8_t attrs() const { return ss().attrs; }
 };
 
-template <typename Outer>
-class MutableStackShapeOperations : public StackShapeOperations<Outer> {
-    StackShape& ss() { return static_cast<Outer*>(this)->get(); }
+template <typename Wrapper>
+class MutableWrappedPtrOperations<StackShape, Wrapper>
+  : public WrappedPtrOperations<StackShape, Wrapper>
+{
+    StackShape& ss() { return static_cast<Wrapper*>(this)->get(); }
 
   public:
     void updateGetterSetter(GetterOp rawGetter, SetterOp rawSetter) {
@@ -1383,19 +1387,6 @@ class MutableStackShapeOperations : public StackShapeOperations<Outer> {
     void setAttrs(uint8_t attrs) { ss().attrs = attrs; }
 };
 
-template <>
-class RootedBase<StackShape> : public MutableStackShapeOperations<JS::Rooted<StackShape>>
-{};
-
-template <>
-class HandleBase<StackShape> : public StackShapeOperations<JS::Handle<StackShape>>
-{};
-
-template <>
-class MutableHandleBase<StackShape>
-  : public MutableStackShapeOperations<JS::MutableHandle<StackShape>>
-{};
-
 inline
 Shape::Shape(const StackShape& other, uint32_t nfixed)
   : base_(other.base),
@@ -1550,38 +1541,6 @@ Shape::matches(const StackShape& other) const
                                 other.rawGetter, other.rawSetter);
 }
 
-// Property lookup hooks on objects are required to return a non-nullptr shape
-// to signify that the property has been found. For cases where the property is
-// not actually represented by a Shape, use a dummy value. This includes all
-// properties of non-native objects, and dense elements for native objects.
-// Use separate APIs for these two cases.
-
-template <AllowGC allowGC>
-static inline void
-MarkNonNativePropertyFound(typename MaybeRooted<Shape*, allowGC>::MutableHandleType propp)
-{
-    propp.set(reinterpret_cast<Shape*>(1));
-}
-
-template <AllowGC allowGC>
-static inline void
-MarkDenseOrTypedArrayElementFound(typename MaybeRooted<Shape*, allowGC>::MutableHandleType propp)
-{
-    propp.set(reinterpret_cast<Shape*>(1));
-}
-
-static inline bool
-IsImplicitDenseOrTypedArrayElement(Shape* prop)
-{
-    return prop == reinterpret_cast<Shape*>(1);
-}
-
-static inline bool
-IsImplicitNonNativeProperty(Shape* prop)
-{
-    return prop == reinterpret_cast<Shape*>(1);
-}
-
 Shape*
 ReshapeForAllocKind(JSContext* cx, Shape* shape, TaggedProto proto,
                     gc::AllocKind allocKind);
diff --git a/js/src/vm/SharedMem.h b/js/src/vm/SharedMem.h
index fe8dad304d..8e5bae492a 100644
--- a/js/src/vm/SharedMem.h
+++ b/js/src/vm/SharedMem.h
@@ -11,8 +11,8 @@
 template<typename T>
 class SharedMem
 {
-    static_assert(mozilla::IsPointer<T>::value,
-                  "SharedMem encapsulates pointer types");
+    // static_assert(mozilla::IsPointer<T>::value,
+    //               "SharedMem encapsulates pointer types");
 
     enum Sharedness {
         IsUnshared,
diff --git a/js/src/vm/String.h b/js/src/vm/String.h
index 0937ac24d2..4c43439cd9 100644
--- a/js/src/vm/String.h
+++ b/js/src/vm/String.h
@@ -521,7 +521,7 @@ class JSString : public js::gc::TenuredCell
     }
 
     static MOZ_ALWAYS_INLINE void writeBarrierPre(JSString* thing) {
-        if (isNullLike(thing) || thing->isPermanentAtom())
+        if (!thing || thing->isPermanentAtom())
             return;
 
         TenuredCell::writeBarrierPre(thing);
diff --git a/js/src/vm/TaggedProto.h b/js/src/vm/TaggedProto.h
index de3e86a7f5..10b8c1171b 100644
--- a/js/src/vm/TaggedProto.h
+++ b/js/src/vm/TaggedProto.h
@@ -68,20 +68,16 @@ struct InternalBarrierMethods<TaggedProto>
 
     static void readBarrier(const TaggedProto& proto);
 
-    static bool isMarkableTaggedPointer(TaggedProto proto) {
-        return proto.isObject();
-    }
-
     static bool isMarkable(TaggedProto proto) {
         return proto.isObject();
     }
 };
 
-template<class Outer>
-class TaggedProtoOperations
+template <class Wrapper>
+class WrappedPtrOperations<TaggedProto, Wrapper>
 {
     const TaggedProto& value() const {
-        return static_cast<const Outer*>(this)->get();
+        return static_cast<const Wrapper*>(this)->get();
     }
 
   public:
@@ -95,18 +91,6 @@ class TaggedProtoOperations
     uint64_t uniqueId() const { return value().uniqueId(); }
 };
 
-template <>
-class HandleBase<TaggedProto> : public TaggedProtoOperations<Handle<TaggedProto>>
-{};
-
-template <>
-class RootedBase<TaggedProto> : public TaggedProtoOperations<Rooted<TaggedProto>>
-{};
-
-template <>
-class BarrieredBaseMixins<TaggedProto> : public TaggedProtoOperations<GCPtr<TaggedProto>>
-{};
-
 // If the TaggedProto is a JSObject pointer, convert to that type and call |f|
 // with the pointer. If the TaggedProto is lazy, calls F::defaultValue.
 template <typename F, typename... Args>
diff --git a/js/src/vm/UnboxedObject.cpp b/js/src/vm/UnboxedObject.cpp
index de6bdef9e3..2ed89e32e4 100644
--- a/js/src/vm/UnboxedObject.cpp
+++ b/js/src/vm/UnboxedObject.cpp
@@ -720,10 +720,10 @@ UnboxedPlainObject::createWithProperties(ExclusiveContext* cx, HandleObjectGroup
 /* static */ bool
 UnboxedPlainObject::obj_lookupProperty(JSContext* cx, HandleObject obj,
                                        HandleId id, MutableHandleObject objp,
-                                       MutableHandleShape propp)
+                                       MutableHandle<PropertyResult> propp)
 {
     if (obj->as<UnboxedPlainObject>().containsUnboxedOrExpandoProperty(cx, id)) {
-        MarkNonNativePropertyFound<CanGC>(propp);
+        propp.setNonNativeProperty();
         objp.set(obj);
         return true;
     }
@@ -731,7 +731,7 @@ UnboxedPlainObject::obj_lookupProperty(JSContext* cx, HandleObject obj,
     RootedObject proto(cx, obj->staticPrototype());
     if (!proto) {
         objp.set(nullptr);
-        propp.set(nullptr);
+        propp.setNotFound();
         return true;
     }
 
@@ -1411,10 +1411,10 @@ UnboxedArrayObject::containsProperty(ExclusiveContext* cx, jsid id)
 /* static */ bool
 UnboxedArrayObject::obj_lookupProperty(JSContext* cx, HandleObject obj,
                                        HandleId id, MutableHandleObject objp,
-                                       MutableHandleShape propp)
+                                       MutableHandle<PropertyResult> propp)
 {
     if (obj->as<UnboxedArrayObject>().containsProperty(cx, id)) {
-        MarkNonNativePropertyFound<CanGC>(propp);
+        propp.setNonNativeProperty();
         objp.set(obj);
         return true;
     }
@@ -1422,7 +1422,7 @@ UnboxedArrayObject::obj_lookupProperty(JSContext* cx, HandleObject obj,
     RootedObject proto(cx, obj->staticPrototype());
     if (!proto) {
         objp.set(nullptr);
-        propp.set(nullptr);
+        propp.setNotFound();
         return true;
     }
 
diff --git a/js/src/vm/UnboxedObject.h b/js/src/vm/UnboxedObject.h
index 8622be8a70..6fc482ec71 100644
--- a/js/src/vm/UnboxedObject.h
+++ b/js/src/vm/UnboxedObject.h
@@ -242,7 +242,7 @@ class UnboxedPlainObject : public JSObject
 
     static bool obj_lookupProperty(JSContext* cx, HandleObject obj,
                                    HandleId id, MutableHandleObject objp,
-                                   MutableHandleShape propp);
+                                   MutableHandle<PropertyResult> propp);
 
     static bool obj_defineProperty(JSContext* cx, HandleObject obj, HandleId id,
                                    Handle<PropertyDescriptor> desc,
@@ -378,7 +378,7 @@ class UnboxedArrayObject : public JSObject
 
     static bool obj_lookupProperty(JSContext* cx, HandleObject obj,
                                    HandleId id, MutableHandleObject objp,
-                                   MutableHandleShape propp);
+                                   MutableHandle<PropertyResult> propp);
 
     static bool obj_defineProperty(JSContext* cx, HandleObject obj, HandleId id,
                                    Handle<PropertyDescriptor> desc,
diff --git a/js/xpconnect/src/XPCInlines.h b/js/xpconnect/src/XPCInlines.h
index ad3d0c7849..e60fac824e 100644
--- a/js/xpconnect/src/XPCInlines.h
+++ b/js/xpconnect/src/XPCInlines.h
@@ -470,7 +470,7 @@ inline
 void XPCWrappedNativeTearOff::JSObjectMoved(JSObject* obj, const JSObject* old)
 {
     MOZ_ASSERT(!IsMarked());
-    MOZ_ASSERT(mJSObject.unbarrieredGetPtr() == old);
+    MOZ_ASSERT(mJSObject == old);
     mJSObject = obj;
 }
 
diff --git a/js/xpconnect/src/XPCWrappedNative.cpp b/js/xpconnect/src/XPCWrappedNative.cpp
index 96f825f05b..2e3419f28a 100644
--- a/js/xpconnect/src/XPCWrappedNative.cpp
+++ b/js/xpconnect/src/XPCWrappedNative.cpp
@@ -935,7 +935,7 @@ void
 XPCWrappedNative::FlatJSObjectMoved(JSObject* obj, const JSObject* old)
 {
     JS::AutoAssertGCCallback inCallback(obj);
-    MOZ_ASSERT(mFlatJSObject.unbarrieredGetPtr() == old);
+    MOZ_ASSERT(mFlatJSObject == old);
 
     nsWrapperCache* cache = nullptr;
     CallQueryInterface(mIdentity, &cache);
diff --git a/js/xpconnect/src/XPCWrappedNativeProto.cpp b/js/xpconnect/src/XPCWrappedNativeProto.cpp
index 6aa023432e..7515ce3f04 100644
--- a/js/xpconnect/src/XPCWrappedNativeProto.cpp
+++ b/js/xpconnect/src/XPCWrappedNativeProto.cpp
@@ -114,7 +114,7 @@ XPCWrappedNativeProto::CallPostCreatePrototype()
 void
 XPCWrappedNativeProto::JSProtoObjectFinalized(js::FreeOp* fop, JSObject* obj)
 {
-    MOZ_ASSERT(obj == mJSProtoObject.unbarrieredGet(), "huh?");
+    MOZ_ASSERT(obj == mJSProtoObject, "huh?");
 
     // Only remove this proto from the map if it is the one in the map.
     ClassInfo2WrappedNativeProtoMap* map = GetScope()->GetWrappedNativeProtoMap();
@@ -129,7 +129,7 @@ XPCWrappedNativeProto::JSProtoObjectFinalized(js::FreeOp* fop, JSObject* obj)
 void
 XPCWrappedNativeProto::JSProtoObjectMoved(JSObject* obj, const JSObject* old)
 {
-    MOZ_ASSERT(mJSProtoObject.unbarrieredGet() == old);
+    MOZ_ASSERT(mJSProtoObject == old);
     mJSProtoObject.init(obj); // Update without triggering barriers.
 }
 
diff --git a/layout/mathml/nsMathMLChar.cpp b/layout/mathml/nsMathMLChar.cpp
index 4b02a52d8d..ad23c57bf5 100644
--- a/layout/mathml/nsMathMLChar.cpp
+++ b/layout/mathml/nsMathMLChar.cpp
@@ -581,9 +581,9 @@ nsOpenTypeTable::MakeTextRun(DrawTarget*        aDrawTarget,
                    aFontGroup->GetFirstValidFont()->
                    GetGlyphHAdvance(aDrawTarget, aGlyph.glyphID));
   detailedGlyph.mXOffset = detailedGlyph.mYOffset = 0;
-  gfxShapedText::CompressedGlyph g;
-  g.SetComplex(true, true, 1);
-  textRun->SetGlyphs(0, g, &detailedGlyph);
+  textRun->SetGlyphs(0,
+                     gfxShapedText::CompressedGlyph::MakeComplex(true, true, 1),
+                     &detailedGlyph);
 
   return textRun.forget();
 }
@@ -1459,7 +1459,7 @@ nsMathMLChar::StretchEnumContext::EnumCallback(const FontFamilyName& aFamily,
   if (!openTypeTable) {
     if (context->mTablesTried.Contains(glyphTable))
       return true; // already tried this one
-    
+
     // Only try this table once.
     context->mTablesTried.AppendElement(glyphTable);
   }
@@ -1626,7 +1626,7 @@ nsMathMLChar::StretchInternal(nsPresContext*           aPresContext,
   if (!maxWidth && !largeop) {
     // Doing Stretch() not GetMaxWidth(),
     // and not a largeop in display mode; we're done if size fits
-    if ((targetSize <= 0) || 
+    if ((targetSize <= 0) ||
         ((isVertical && charSize >= targetSize) ||
          IsSizeOK(charSize, targetSize, aStretchHint)))
       done = true;
@@ -1678,7 +1678,7 @@ nsMathMLChar::StretchInternal(nsPresContext*           aPresContext,
     // variables accordingly.
     mUnscaledAscent = aDesiredStretchSize.ascent;
   }
-    
+
   if (glyphFound) {
     return NS_OK;
   }
@@ -1695,7 +1695,7 @@ nsMathMLChar::StretchInternal(nsPresContext*           aPresContext,
   if (!Preferences::GetBool("mathml.scale_stretchy_operators.enabled", true)) {
     return NS_OK;
   }
-  
+
   // stretchy character
   if (stretchy) {
     if (isVertical) {
@@ -1863,7 +1863,7 @@ public:
   nsDisplayMathMLCharForeground(nsDisplayListBuilder* aBuilder,
                                 nsIFrame* aFrame, nsMathMLChar* aChar,
 				                uint32_t aIndex, bool aIsSelected)
-    : nsDisplayItem(aBuilder, aFrame), mChar(aChar), 
+    : nsDisplayItem(aBuilder, aFrame), mChar(aChar),
       mIndex(aIndex), mIsSelected(aIsSelected) {
     MOZ_COUNT_CTOR(nsDisplayMathMLCharForeground);
   }
@@ -1886,7 +1886,7 @@ public:
     temp.Inflate(mFrame->PresContext()->AppUnitsPerDevPixel());
     return temp;
   }
-  
+
   virtual void Paint(nsDisplayListBuilder* aBuilder,
                      nsRenderingContext* aCtx) override
   {
@@ -1901,7 +1901,7 @@ public:
     bool snap;
     return GetBounds(aBuilder, &snap);
   }
-  
+
   virtual uint32_t GetPerFrameKey() override {
     return (mIndex << nsDisplayItem::TYPE_BITS)
       | nsDisplayItem::GetPerFrameKey();
@@ -2355,7 +2355,7 @@ nsMathMLChar::PaintHorizontally(nsPresContext* aPresContext,
     // _cairo_scaled_font_glyph_device_extents rounds outwards to the nearest
     // pixel, so the bm values can include 1 row of faint pixels on each edge.
     // Don't rely on this pixel as it can look like a gap.
-    if (bm.rightBearing - bm.leftBearing >= 2 * oneDevPixel) { 
+    if (bm.rightBearing - bm.leftBearing >= 2 * oneDevPixel) {
       start[i] = dx + bm.leftBearing + oneDevPixel; // left join
       end[i] = dx + bm.rightBearing - oneDevPixel; // right join
     } else {
diff --git a/netwerk/base/nsSocketTransport2.cpp b/netwerk/base/nsSocketTransport2.cpp
index 037b1a8829..d6b713fe6e 100644
--- a/netwerk/base/nsSocketTransport2.cpp
+++ b/netwerk/base/nsSocketTransport2.cpp
@@ -931,7 +931,6 @@ nsresult
 nsSocketTransport::InitWithConnectedSocket(PRFileDesc *fd, const NetAddr *addr)
 {
     MOZ_ASSERT(PR_GetCurrentThread() == gSocketThread, "wrong thread");
-    NS_ASSERTION(!mFD.IsInitialized(), "already initialized");
 
     char buf[kNetAddrMaxCStrBufSize];
     NetAddrToString(addr, buf, sizeof(buf));
@@ -957,6 +956,7 @@ nsSocketTransport::InitWithConnectedSocket(PRFileDesc *fd, const NetAddr *addr)
     {
         MutexAutoLock lock(mLock);
 
+        NS_ASSERTION(!mFD.IsInitialized(), "already initialized");
         mFD = fd;
         mFDref = 1;
         mFDconnected = 1;
@@ -1320,11 +1320,14 @@ nsSocketTransport::InitiateSocket()
     //
     // if we already have a connected socket, then just attach and return.
     //
-    if (mFD.IsInitialized()) {
+    {
+      MutexAutoLock lock(mLock);
+      if (mFD.IsInitialized()) {
         rv = mSocketTransportService->AttachSocket(mFD, this);
         if (NS_SUCCEEDED(rv))
-            mAttached = true;
+          mAttached = true;
         return rv;
+      }
     }
 
     //
@@ -1390,18 +1393,18 @@ nsSocketTransport::InitiateSocket()
     PR_SetSocketOption(fd, &opt);
 #endif
 
-    // inform socket transport about this newly created socket...
-    rv = mSocketTransportService->AttachSocket(fd, this);
-    if (NS_FAILED(rv)) {
-        CloseSocket(fd);
-        return rv;
-    }
-    mAttached = true;
-
     // assign mFD so that we can properly handle OnSocketDetached before we've
     // established a connection.
     {
         MutexAutoLock lock(mLock);
+        // inform socket transport about this newly created socket...
+        rv = mSocketTransportService->AttachSocket(fd, this);
+        if (NS_FAILED(rv)) {
+            CloseSocket(fd);
+            return rv;
+        }
+        mAttached = true;
+
         mFD = fd;
         mFDref = 1;
         mFDconnected = false;
@@ -1546,8 +1549,12 @@ nsSocketTransport::RecoverFromError()
 
     nsresult rv;
 
-    // OK to check this outside mLock
-    NS_ASSERTION(!mFDconnected, "socket should not be connected");
+#ifdef DEBUG
+    {
+      MutexAutoLock lock(mLock);
+      NS_ASSERTION(!mFDconnected, "socket should not be connected");
+    }
+#endif
 
     // all connection failures need to be reported to DNS so that the next
     // time we will use a different address if available.
diff --git a/netwerk/base/nsSocketTransport2.h b/netwerk/base/nsSocketTransport2.h
index cb107e6e79..89b75efa57 100644
--- a/netwerk/base/nsSocketTransport2.h
+++ b/netwerk/base/nsSocketTransport2.h
@@ -350,11 +350,13 @@ private:
 
     void OnMsgInputPending()
     {
+        MOZ_ASSERT(OnSocketThread(), "not on socket thread");
         if (mState == STATE_TRANSFERRING)
             mPollFlags |= (PR_POLL_READ | PR_POLL_EXCEPT);
     }
     void OnMsgOutputPending()
     {
+        MOZ_ASSERT(OnSocketThread(), "not on socket thread");
         if (mState == STATE_TRANSFERRING)
             mPollFlags |= (PR_POLL_WRITE | PR_POLL_EXCEPT);
     }
diff --git a/toolkit/mozapps/extensions/internal/AddonUpdateChecker.jsm b/toolkit/mozapps/extensions/internal/AddonUpdateChecker.jsm
index a475f7f1fa..6710c6a70f 100644
--- a/toolkit/mozapps/extensions/internal/AddonUpdateChecker.jsm
+++ b/toolkit/mozapps/extensions/internal/AddonUpdateChecker.jsm
@@ -611,6 +611,14 @@ function UpdateParser(aId, aUpdateKey, aUrl, aObserver) {
   let requireBuiltIn = Services.prefs.getBoolPref(PREF_UPDATE_REQUIREBUILTINCERTS, true);
 
   logger.debug("Requesting " + aUrl);
+
+  if (!aUrl) {
+    logger.warn("Request failed: empty update manifest URL");
+    this._doneAt = new Error("UP_emptyManifestURL");
+    this.notifyError(AddonUpdateChecker.ERROR_DOWNLOAD_ERROR);
+    return;
+  }
+
   try {
     this.request = new ServiceRequest();
     this.request.open("GET", this.url, true);
diff --git a/toolkit/mozapps/extensions/internal/XPIProvider.jsm b/toolkit/mozapps/extensions/internal/XPIProvider.jsm
index 690351be1d..8eb140f0c6 100644
--- a/toolkit/mozapps/extensions/internal/XPIProvider.jsm
+++ b/toolkit/mozapps/extensions/internal/XPIProvider.jsm
@@ -6135,7 +6135,11 @@ function UpdateChecker(aAddon, aListener, aReason, aAppVersion, aPlatformVersion
   if ("onUpdateAvailable" in this.listener)
     aReason |= UPDATE_TYPE_NEWVERSION;
 
-  let url = escapeAddonURI(aAddon, updateURL, aReason, aAppVersion);
+  // Don't perform substitutions on the update URL if we still don't
+  // have one at this point.
+  let url = updateURL ?
+            escapeAddonURI(aAddon, url, aReason, aAppVersion) :
+            updateURL;
   this._parser = AddonUpdateChecker.checkForUpdates(aAddon.id, aAddon.updateKey,
                                                     url, this);
 }
diff --git a/widget/nsITransferable.idl b/widget/nsITransferable.idl
index b128586dd1..e580673f5e 100644
--- a/widget/nsITransferable.idl
+++ b/widget/nsITransferable.idl
@@ -13,12 +13,17 @@ interface nsIPrincipal;
 
 %{ C++
 
+// Internal formats must have their second part starting with 'x-moz-',
+// for example text/x-moz-internaltype. These cannot be assigned by
+// unprivileged content but all other types can.
+#define kInternal_Mimetype_Prefix   "/x-moz-"
+
 // these probably shouldn't live here, but in some central repository shared
 // by the entire app.
 #define kTextMime                   "text/plain"
 #define kRTFMime                    "text/rtf"
 #define kUnicodeMime                "text/unicode"
-#define kMozTextInternal          "text/x-moz-text-internal"  // text data which isn't suppoed to be parsed by other apps.
+#define kMozTextInternal            "text/x-moz-text-internal"  // text data which isn't suppoed to be parsed by other apps.
 #define kHTMLMime                   "text/html"
 #define kAOLMailMime                "AOLMAIL"
 #define kPNGImageMime               "image/png"