diff --git a/dom/base/ShadowRoot.cpp b/dom/base/ShadowRoot.cpp
index b809110b2b..2f24c2856f 100644
--- a/dom/base/ShadowRoot.cpp
+++ b/dom/base/ShadowRoot.cpp
@@ -110,7 +110,7 @@ ShadowRoot::CloneInternalDataFrom(ShadowRoot* aOther)
     StyleSheet* sheet = aOther->SheetAt(i);
     if (sheet && sheet->IsApplicable()) {
       RefPtr<CSSStyleSheet> clonedSheet =
-        sheet->AsGecko()->Clone(nullptr, nullptr, nullptr, nullptr);
+        sheet->AsConcrete()->Clone(nullptr, nullptr, nullptr, nullptr);
       if (clonedSheet) {
         AppendStyleSheet(*clonedSheet);
       }
diff --git a/dom/base/nsDocument.cpp b/dom/base/nsDocument.cpp
index a5b67b6b13..5f1d3a30c0 100644
--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -1150,7 +1150,7 @@ nsDOMStyleSheetSetList::EnsureFresh()
   for (size_t index = 0; index < count; index++) {
     StyleSheet* sheet = mDocument->SheetAt(index);
     NS_ASSERTION(sheet, "Null sheet in sheet list!");
-    sheet->AsGecko()->GetTitle(title);
+    sheet->AsConcrete()->GetTitle(title);
     if (!title.IsEmpty() && !mNames.Contains(title) && !Add(title)) {
       return;
     }
@@ -2071,7 +2071,7 @@ nsDocument::RemoveDocStyleSheetsFromStyleSets()
     if (sheet->IsApplicable()) {
       nsCOMPtr<nsIPresShell> shell = GetShell();
       if (shell) {
-        shell->StyleSet()->RemoveDocStyleSheet(sheet->AsGecko());
+        shell->StyleSet()->RemoveDocStyleSheet(sheet->AsConcrete());
       }
     }
     // XXX Tell observers?
@@ -2090,7 +2090,7 @@ nsDocument::RemoveStyleSheetsFromStyleSets(
     if (sheet->IsApplicable()) {
       nsCOMPtr<nsIPresShell> shell = GetShell();
       if (shell) {
-        shell->StyleSet()->RemoveStyleSheet(aType, sheet->AsGecko());
+        shell->StyleSet()->RemoveStyleSheet(aType, sheet->AsConcrete());
       }
     }
     // XXX Tell observers?
@@ -2161,7 +2161,7 @@ AppendSheetsToStyleSet(nsStyleSet* aStyleSet,
                        SheetType aType)
 {
   for (StyleSheet* sheet : Reversed(aSheets)) {
-    aStyleSet->AppendStyleSheet(aType, sheet->AsGecko());
+    aStyleSet->AppendStyleSheet(aType, sheet->AsConcrete());
   }
 }
 
@@ -2177,21 +2177,21 @@ nsDocument::FillStyleSet(nsStyleSet* aStyleSet)
 
   for (StyleSheet* sheet : Reversed(mStyleSheets)) {
     if (sheet->IsApplicable()) {
-      aStyleSet->AddDocStyleSheet(sheet->AsGecko(), this);
+      aStyleSet->AddDocStyleSheet(sheet->AsConcrete(), this);
     }
   }
 
   nsStyleSheetService *sheetService = nsStyleSheetService::GetInstance();
   if (sheetService) {
     for (StyleSheet* sheet : *sheetService->AuthorStyleSheets()) {
-      aStyleSet->AppendStyleSheet(SheetType::Doc, sheet->AsGecko());
+      aStyleSet->AppendStyleSheet(SheetType::Doc, sheet->AsConcrete());
     }
   }
 
   // Iterate backwards to maintain order
   for (StyleSheet* sheet : Reversed(mOnDemandBuiltInUASheets)) {
     if (sheet->IsApplicable()) {
-      aStyleSet->PrependStyleSheet(SheetType::Agent, sheet->AsGecko());
+      aStyleSet->PrependStyleSheet(SheetType::Agent, sheet->AsConcrete());
     }
   }
 
@@ -3807,7 +3807,7 @@ nsDocument::AddOnDemandBuiltInUASheet(StyleSheet* aSheet)
       // do not override Firefox OS/Mobile's content.css sheet. Maybe we should
       // have an insertion point to match the order of
       // nsDocumentViewer::CreateStyleSet though?
-      shell->StyleSet()->PrependStyleSheet(SheetType::Agent, aSheet->AsGecko());
+      shell->StyleSet()->PrependStyleSheet(SheetType::Agent, aSheet->AsConcrete());
     }
   }
 
@@ -3819,7 +3819,7 @@ nsDocument::AddStyleSheetToStyleSets(StyleSheet* aSheet)
 {
   nsCOMPtr<nsIPresShell> shell = GetShell();
   if (shell) {
-    shell->StyleSet()->AddDocStyleSheet(aSheet->AsGecko(), this);
+    shell->StyleSet()->AddDocStyleSheet(aSheet->AsConcrete(), this);
   }
 }
 
@@ -3828,7 +3828,7 @@ nsDocument::AddStyleSheetToStyleSets(StyleSheet* aSheet)
     className##Init init;                                                     \
     init.mBubbles = true;                                                     \
     init.mCancelable = true;                                                  \
-    init.mStylesheet = aSheet->AsGecko();                                     \
+    init.mStylesheet = aSheet->AsConcrete();                                  \
     init.memberName = argName;                                                \
                                                                               \
     RefPtr<className> event =                                               \
@@ -3886,7 +3886,7 @@ nsDocument::RemoveStyleSheetFromStyleSets(StyleSheet* aSheet)
 {
   nsCOMPtr<nsIPresShell> shell = GetShell();
   if (shell) {
-    shell->StyleSet()->RemoveDocStyleSheet(aSheet->AsGecko());
+    shell->StyleSet()->RemoveDocStyleSheet(aSheet->AsConcrete());
   }
 }
 
@@ -4102,7 +4102,7 @@ nsDocument::AddAdditionalStyleSheet(additionalSheetType aType, StyleSheet* aShee
   nsCOMPtr<nsIPresShell> shell = GetShell();
   if (shell) {
     SheetType type = ConvertAdditionalSheetType(aType);
-    shell->StyleSet()->AppendStyleSheet(type, aSheet->AsGecko());
+    shell->StyleSet()->AppendStyleSheet(type, aSheet->AsConcrete());
   }
 
   // Passing false, so documet.styleSheets.length will not be affected by
@@ -4130,7 +4130,7 @@ nsDocument::RemoveAdditionalStyleSheet(additionalSheetType aType, nsIURI* aSheet
       nsCOMPtr<nsIPresShell> shell = GetShell();
       if (shell) {
         SheetType type = ConvertAdditionalSheetType(aType);
-        shell->StyleSet()->RemoveStyleSheet(type, sheetRef->AsGecko());
+        shell->StyleSet()->RemoveStyleSheet(type, sheetRef->AsConcrete());
       }
     }
 
@@ -5598,13 +5598,13 @@ nsIDocument::GetSelectedStyleSheetSet(nsAString& aSheetSet)
     NS_ASSERTION(sheet, "Null sheet in sheet list!");
 
     bool disabled;
-    sheet->AsGecko()->GetDisabled(&disabled);
+    sheet->AsConcrete()->GetDisabled(&disabled);
     if (disabled) {
       // Disabled sheets don't affect the currently selected set
       continue;
     }
 
-    sheet->AsGecko()->GetTitle(title);
+    sheet->AsConcrete()->GetTitle(title);
 
     if (aSheetSet.IsEmpty()) {
       aSheetSet = title;
@@ -5711,9 +5711,9 @@ nsDocument::EnableStyleSheetsForSetInternal(const nsAString& aSheetSet,
     StyleSheet* sheet = SheetAt(index);
     NS_ASSERTION(sheet, "Null sheet in sheet list!");
 
-    sheet->AsGecko()->GetTitle(title);
+    sheet->AsConcrete()->GetTitle(title);
     if (!title.IsEmpty()) {
-      sheet->AsGecko()->SetEnabled(title.Equals(aSheetSet));
+      sheet->AsConcrete()->SetEnabled(title.Equals(aSheetSet));
     }
   }
   if (aUpdateCSSLoader) {
@@ -9434,7 +9434,7 @@ nsIDocument::CreateStaticClone(nsIDocShell* aCloneContainer)
         if (sheet) {
           if (sheet->IsApplicable()) {
             RefPtr<CSSStyleSheet> clonedSheet =
-              sheet->AsGecko()->Clone(nullptr, nullptr, clonedDoc, nullptr);
+              sheet->AsConcrete()->Clone(nullptr, nullptr, clonedDoc, nullptr);
             NS_WARNING_ASSERTION(clonedSheet,
                                  "Cloning a stylesheet didn't work!");
             if (clonedSheet) {
@@ -9449,7 +9449,7 @@ nsIDocument::CreateStaticClone(nsIDocShell* aCloneContainer)
         if (sheet) {
           if (sheet->IsApplicable()) {
             RefPtr<CSSStyleSheet> clonedSheet =
-              sheet->AsGecko()->Clone(nullptr, nullptr, clonedDoc, nullptr);
+              sheet->AsConcrete()->Clone(nullptr, nullptr, clonedDoc, nullptr);
             NS_WARNING_ASSERTION(clonedSheet,
                                  "Cloning a stylesheet didn't work!");
             if (clonedSheet) {
diff --git a/dom/base/nsStyleLinkElement.cpp b/dom/base/nsStyleLinkElement.cpp
index 707d36a510..7a0a563350 100644
--- a/dom/base/nsStyleLinkElement.cpp
+++ b/dom/base/nsStyleLinkElement.cpp
@@ -321,7 +321,7 @@ nsStyleLinkElement::DoUpdateStyleSheet(nsIDocument* aOldDocument,
 
   Element* oldScopeElement = nullptr;
   if (mStyleSheet) {
-    oldScopeElement = mStyleSheet->AsGecko()->GetScopeElement();
+    oldScopeElement = mStyleSheet->AsConcrete()->GetScopeElement();
   }
 
   if (mStyleSheet && (aOldDocument || aOldShadowRoot)) {
@@ -483,7 +483,7 @@ nsStyleLinkElement::UpdateStyleSheetScopedness(bool aIsNowScoped)
     return;
   }
 
-  CSSStyleSheet* sheet = mStyleSheet->AsGecko();
+  CSSStyleSheet* sheet = mStyleSheet->AsConcrete();
 
   nsCOMPtr<nsIContent> thisContent;
   CallQueryInterface(this, getter_AddRefs(thisContent));
diff --git a/dom/xbl/nsXBLPrototypeResources.cpp b/dom/xbl/nsXBLPrototypeResources.cpp
index bbeb44362b..c69b6e2988 100644
--- a/dom/xbl/nsXBLPrototypeResources.cpp
+++ b/dom/xbl/nsXBLPrototypeResources.cpp
@@ -147,7 +147,7 @@ nsXBLPrototypeResources::GatherRuleProcessor()
 {
   nsTArray<RefPtr<CSSStyleSheet>> sheets(mStyleSheetList.Length());
   for (StyleSheet* sheet : mStyleSheetList) {
-    sheets.AppendElement(sheet->AsGecko());
+    sheets.AppendElement(sheet->AsConcrete());
   }
   mRuleProcessor = new nsCSSRuleProcessor(Move(sheets),
                                           SheetType::Doc,
diff --git a/editor/libeditor/HTMLEditor.cpp b/editor/libeditor/HTMLEditor.cpp
index f73c2cbba0..cddf9b749d 100644
--- a/editor/libeditor/HTMLEditor.cpp
+++ b/editor/libeditor/HTMLEditor.cpp
@@ -2907,7 +2907,7 @@ HTMLEditor::EnableStyleSheet(const nsAString& aURL,
   nsCOMPtr<nsIDocument> document = GetDocument();
   sheet->SetAssociatedDocument(document, StyleSheet::NotOwnedByDocument);
 
-  return sheet->AsGecko()->SetDisabled(!aEnable);
+  return sheet->AsConcrete()->SetDisabled(!aEnable);
 }
 
 bool
@@ -2924,7 +2924,7 @@ HTMLEditor::EnableExistingStyleSheet(const nsAString& aURL)
   nsCOMPtr<nsIDocument> document = GetDocument();
   sheet->SetAssociatedDocument(document, StyleSheet::NotOwnedByDocument);
 
-  sheet->AsGecko()->SetDisabled(false);
+  sheet->AsConcrete()->SetDisabled(false);
   return true;
 }
 
diff --git a/layout/base/nsDocumentViewer.cpp b/layout/base/nsDocumentViewer.cpp
index 75d42ebe04..ac48fa6656 100644
--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@@ -2306,7 +2306,7 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument)
   }
 
   if (sheet)
-    styleSet->AppendStyleSheet(SheetType::User, sheet->AsGecko());
+    styleSet->AppendStyleSheet(SheetType::User, sheet->AsConcrete());
 
   // Append chrome sheets (scrollbars + forms).
   bool shouldOverride = false;
@@ -2342,7 +2342,7 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument)
           cssLoader->LoadSheetSync(uri, &chromeSheet);
           if (!chromeSheet) continue;
 
-          styleSet->PrependStyleSheet(SheetType::Agent, chromeSheet->AsGecko());
+          styleSet->PrependStyleSheet(SheetType::Agent, chromeSheet->AsConcrete());
           shouldOverride = true;
         }
         free(str);
@@ -2353,7 +2353,7 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument)
   if (!shouldOverride) {
     sheet = cache->ScrollbarsSheet();
     if (sheet) {
-      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsGecko());
+      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsConcrete());
     }
   }
 
@@ -2369,12 +2369,12 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument)
 
     sheet = cache->NumberControlSheet();
     if (sheet) {
-      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsGecko());
+      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsConcrete());
     }
 
     sheet = cache->FormsSheet();
     if (sheet) {
-      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsGecko());
+      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsConcrete());
     }
 
     if (aDocument->LoadsFullXULStyleSheetUpFront()) {
@@ -2382,7 +2382,7 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument)
       // up-front here.
       sheet = cache->XULSheet();
       if (sheet) {
-        styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsGecko());
+        styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsConcrete());
       }
     }
 
@@ -2390,25 +2390,25 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument)
     if (sheet) {
       // Load the minimal XUL rules for scrollbars and a few other XUL things
       // that non-XUL (typically HTML) documents commonly use.
-      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsGecko());
+      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsConcrete());
     }
 
     sheet = cache->CounterStylesSheet();
     if (sheet) {
-      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsGecko());
+      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsConcrete());
     }
 
     if (nsLayoutUtils::ShouldUseNoScriptSheet(aDocument)) {
       sheet = cache->NoScriptSheet();
       if (sheet) {
-        styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsGecko());
+        styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsConcrete());
       }
     }
 
     if (nsLayoutUtils::ShouldUseNoFramesSheet(aDocument)) {
       sheet = cache->NoFramesSheet();
       if (sheet) {
-        styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsGecko());
+        styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsConcrete());
       }
     }
 
@@ -2417,26 +2417,26 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument)
 
     sheet = cache->HTMLSheet();
     if (sheet) {
-      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsGecko());
+      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsConcrete());
     }
 
     styleSet->PrependStyleSheet(SheetType::Agent,
-                                cache->UASheet()->AsGecko());
+                                cache->UASheet()->AsConcrete());
   } else {
     // SVG documents may have scrollbars and need the scrollbar styling.
     sheet = cache->MinimalXULSheet();
     if (sheet) {
-      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsGecko());
+      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsConcrete());
     }
   }
 
   nsStyleSheetService* sheetService = nsStyleSheetService::GetInstance();
   if (sheetService) {
     for (StyleSheet* sheet : *sheetService->AgentStyleSheets()) {
-      styleSet->AppendStyleSheet(SheetType::Agent, sheet->AsGecko());
+      styleSet->AppendStyleSheet(SheetType::Agent, sheet->AsConcrete());
     }
     for (StyleSheet* sheet : Reversed(*sheetService->UserStyleSheets())) {
-      styleSet->PrependStyleSheet(SheetType::User, sheet->AsGecko());
+      styleSet->PrependStyleSheet(SheetType::User, sheet->AsConcrete());
     }
   }
 
diff --git a/layout/base/nsPresContext.cpp b/layout/base/nsPresContext.cpp
index 65f221a8ae..ff7cefb111 100644
--- a/layout/base/nsPresContext.cpp
+++ b/layout/base/nsPresContext.cpp
@@ -1146,11 +1146,11 @@ nsPresContext::CompatibilityModeChanged()
   if (needsQuirkSheet) {
     // quirk.css needs to come after html.css; we just keep it at the end.
     DebugOnly<nsresult> rv =
-      styleSet->AppendStyleSheet(SheetType::Agent, sheet->AsGecko());
+      styleSet->AppendStyleSheet(SheetType::Agent, sheet->AsConcrete());
     NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "failed to insert quirk.css");
   } else {
     DebugOnly<nsresult> rv =
-      styleSet->RemoveStyleSheet(SheetType::Agent, sheet->AsGecko());
+      styleSet->RemoveStyleSheet(SheetType::Agent, sheet->AsConcrete());
     NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "failed to remove quirk.css");
   }
 
diff --git a/layout/base/nsPresShell.cpp b/layout/base/nsPresShell.cpp
index 0a9627bc9b..713b06cb96 100644
--- a/layout/base/nsPresShell.cpp
+++ b/layout/base/nsPresShell.cpp
@@ -1397,7 +1397,7 @@ PresShell::UpdatePreferenceStyles()
 
   RemovePreferenceStyles();
 
-  mStyleSet->AppendStyleSheet(SheetType::User, newPrefSheet->AsGecko());
+  mStyleSet->AppendStyleSheet(SheetType::User, newPrefSheet->AsConcrete());
   mPrefStyleSheet = newPrefSheet;
 
   mStyleSet->EndUpdate();
@@ -1407,7 +1407,7 @@ void
 PresShell::RemovePreferenceStyles()
 {
   if (mPrefStyleSheet) {
-    mStyleSet->RemoveStyleSheet(SheetType::User, mPrefStyleSheet->AsGecko());
+    mStyleSet->RemoveStyleSheet(SheetType::User, mPrefStyleSheet->AsConcrete());
     mPrefStyleSheet = nullptr;
   }
 }
@@ -1430,13 +1430,13 @@ PresShell::AddUserSheet(nsISupports* aSheet)
   // Iterate forwards when removing so the searches for RemoveStyleSheet are as
   // short as possible.
   for (StyleSheet* sheet : userSheets) {
-    mStyleSet->RemoveStyleSheet(SheetType::User, sheet->AsGecko());
+    mStyleSet->RemoveStyleSheet(SheetType::User, sheet->AsConcrete());
   }
 
   // Now iterate backwards, so that the order of userSheets will be the same as
   // the order of sheets from it in the style set.
   for (StyleSheet* sheet : Reversed(userSheets)) {
-    mStyleSet->PrependStyleSheet(SheetType::User, sheet->AsGecko());
+    mStyleSet->PrependStyleSheet(SheetType::User, sheet->AsConcrete());
   }
 
   mStyleSet->EndUpdate();
@@ -1454,7 +1454,7 @@ PresShell::AddAgentSheet(nsISupports* aSheet)
     return;
   }
 
-  mStyleSet->AppendStyleSheet(SheetType::Agent, sheet->AsGecko());
+  mStyleSet->AppendStyleSheet(SheetType::Agent, sheet->AsConcrete());
   RestyleForCSSRuleChanges();
 }
 
@@ -1471,9 +1471,9 @@ PresShell::AddAuthorSheet(nsISupports* aSheet)
   StyleSheet* firstAuthorSheet =
     mDocument->GetFirstAdditionalAuthorSheet();
   if (firstAuthorSheet) {
-    mStyleSet->InsertStyleSheetBefore(SheetType::Doc, sheet->AsGecko(), firstAuthorSheet->AsGecko());
+    mStyleSet->InsertStyleSheetBefore(SheetType::Doc, sheet->AsConcrete(), firstAuthorSheet->AsConcrete());
   } else {
-    mStyleSet->AppendStyleSheet(SheetType::Doc, sheet->AsGecko());
+    mStyleSet->AppendStyleSheet(SheetType::Doc, sheet->AsConcrete());
   }
 
   RestyleForCSSRuleChanges();
@@ -1487,7 +1487,7 @@ PresShell::RemoveSheet(SheetType aType, nsISupports* aSheet)
     return;
   }
 
-  mStyleSet->RemoveStyleSheet(aType, sheet->AsGecko());
+  mStyleSet->RemoveStyleSheet(aType, sheet->AsConcrete());
   RestyleForCSSRuleChanges();
 }
 
@@ -4471,7 +4471,7 @@ PresShell::RecordStyleSheetChange(StyleSheet* aStyleSheet)
   if (mStylesHaveChanged)
     return;
 
-  Element* scopeElement = aStyleSheet->AsGecko()->GetScopeElement();
+  Element* scopeElement = aStyleSheet->AsConcrete()->GetScopeElement();
   if (scopeElement) {
     mChangedScopeStyleRoots.AppendElement(scopeElement);
     return;
@@ -8771,7 +8771,7 @@ PresShell::SetAgentStyleSheets(const nsTArray<RefPtr<StyleSheet>>& aSheets)
 {
   nsTArray<RefPtr<CSSStyleSheet>> newSheets(aSheets.Length());
   for (auto& sheet : aSheets) {
-    newSheets.AppendElement(sheet->AsGecko());
+    newSheets.AppendElement(sheet->AsConcrete());
   }
   return mStyleSet->ReplaceSheets(SheetType::Agent, newSheets);
 }
@@ -8779,13 +8779,13 @@ PresShell::SetAgentStyleSheets(const nsTArray<RefPtr<StyleSheet>>& aSheets)
 nsresult
 PresShell::AddOverrideStyleSheet(StyleSheet* aSheet)
 {
-  return mStyleSet->PrependStyleSheet(SheetType::Override, aSheet->AsGecko());
+  return mStyleSet->PrependStyleSheet(SheetType::Override, aSheet->AsConcrete());
 }
 
 nsresult
 PresShell::RemoveOverrideStyleSheet(StyleSheet* aSheet)
 {
-  return mStyleSet->RemoveStyleSheet(SheetType::Override, aSheet->AsGecko());
+  return mStyleSet->RemoveStyleSheet(SheetType::Override, aSheet->AsConcrete());
 }
 
 static void
diff --git a/layout/base/nsStyleSheetService.cpp b/layout/base/nsStyleSheetService.cpp
index 6ff54462ee..ac2d430552 100644
--- a/layout/base/nsStyleSheetService.cpp
+++ b/layout/base/nsStyleSheetService.cpp
@@ -177,7 +177,7 @@ nsStyleSheetService::LoadAndRegisterSheet(nsIURI *aSheetURI,
       // mSheets[aSheetType]
 
       StyleSheet* sheet = mSheets[aSheetType].LastElement();
-      CSSStyleSheet* cssSheet = sheet->AsGecko();
+      CSSStyleSheet* cssSheet = sheet->AsConcrete();
       serv->NotifyObservers(NS_ISUPPORTS_CAST(nsIDOMCSSStyleSheet*, cssSheet),
                             message, nullptr);
     }
@@ -283,7 +283,7 @@ nsStyleSheetService::PreloadSheet(nsIURI *aSheetURI, uint32_t aSheetType,
   nsresult rv = loader->LoadSheetSync(aSheetURI, parsingMode, true, &sheet);
   NS_ENSURE_SUCCESS(rv, rv);
 
-  RefPtr<CSSStyleSheet> cssSheet = sheet->AsGecko();
+  RefPtr<CSSStyleSheet> cssSheet = sheet->AsConcrete();
   cssSheet.forget(aSheet);
 
   return NS_OK;
@@ -317,7 +317,7 @@ nsStyleSheetService::UnregisterSheet(nsIURI *aSheetURI, uint32_t aSheetType)
 
   nsCOMPtr<nsIObserverService> serv = services::GetObserverService();
   if (serv) {
-    CSSStyleSheet* cssSheet = sheet->AsGecko();
+    CSSStyleSheet* cssSheet = sheet->AsConcrete();
     serv->NotifyObservers(NS_ISUPPORTS_CAST(nsIDOMCSSStyleSheet*, cssSheet),
                           message, nullptr);
   }
diff --git a/layout/style/CSSStyleSheet.cpp b/layout/style/CSSStyleSheet.cpp
index 1cb99ec001..5b8a9912fc 100644
--- a/layout/style/CSSStyleSheet.cpp
+++ b/layout/style/CSSStyleSheet.cpp
@@ -1929,7 +1929,7 @@ CSSStyleSheet::StyleSheetLoaded(StyleSheet* aSheet,
                                 bool aWasAlternate,
                                 nsresult aStatus)
 {
-  CSSStyleSheet* sheet = aSheet->AsGecko();
+  CSSStyleSheet* sheet = aSheet->AsConcrete();
 
   if (sheet->GetParentSheet() == nullptr) {
     return NS_OK; // ignore if sheet has been detached already (see parseSheet)
diff --git a/layout/style/DeprecatedUtils.h b/layout/style/DeprecatedUtils.h
deleted file mode 100644
index 0484b6dbb3..0000000000
--- a/layout/style/DeprecatedUtils.h
+++ /dev/null
@@ -1,33 +0,0 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-/* some deprecated utilities */
-
-#ifndef mozilla_DeprecatedUtils_h
-#define mozilla_DeprecatedUtils_h
-
-#include "mozilla/TypeTraits.h"
-
-/**
- * Macro used in a base class of |geckotype_|.
- */
-#define MOZ_DECL_DEPRECATED_METHODS(geckotype_)  \
-  inline geckotype_* AsGecko();                         \
-  inline const geckotype_* AsGecko() const;
-
-/**
- * Macro used in inline header of class |type_| with its Gecko
- * subclass named |geckotype_| for implementing the inline methods
- * defined by MOZ_DECL_DEPRECATED_METHODS.
- */
-#define MOZ_DEFINE_DEPRECATED_METHODS(type_, geckotype_) \
-  geckotype_* type_::AsGecko() {                                \
-    return static_cast<geckotype_*>(this);                      \
-  }                                                             \
-  const geckotype_* type_::AsGecko() const {                    \
-    return static_cast<const geckotype_*>(this);                \
-  }
-
-#endif // mozilla_DeprecatedUtils_h
diff --git a/layout/style/Loader.cpp b/layout/style/Loader.cpp
index f7777a1fa8..4e1a1d6fe1 100644
--- a/layout/style/Loader.cpp
+++ b/layout/style/Loader.cpp
@@ -1130,11 +1130,11 @@ Loader::CreateSheet(nsIURI* aURI,
     if (sheet) {
       // This sheet came from the XUL cache or our per-document hashtable; it
       // better be a complete sheet.
-      NS_ASSERTION(sheet->AsGecko()->IsComplete(),
+      NS_ASSERTION(sheet->AsConcrete()->IsComplete(),
                    "Sheet thinks it's not complete while we think it is");
 
       // Make sure it hasn't been modified; if it has, we can't use it
-      if (sheet->AsGecko()->IsModified()) {
+      if (sheet->AsConcrete()->IsModified()) {
         LOG(("  Not cloning completed sheet %p because it's been modified",
              sheet.get()));
         sheet = nullptr;
@@ -1187,25 +1187,25 @@ Loader::CreateSheet(nsIURI* aURI,
 
     if (sheet) {
       // The sheet we have now should be either incomplete or unmodified
-      NS_ASSERTION(!sheet->AsGecko()->IsModified() ||
-                   !sheet->AsGecko()->IsComplete(),
+      NS_ASSERTION(!sheet->AsConcrete()->IsModified() ||
+                   !sheet->AsConcrete()->IsComplete(),
                    "Unexpected modified complete sheet");
-      NS_ASSERTION(sheet->AsGecko()->IsComplete() ||
+      NS_ASSERTION(sheet->AsConcrete()->IsComplete() ||
                    aSheetState != eSheetComplete,
                    "Sheet thinks it's not complete while we think it is");
 
       RefPtr<CSSStyleSheet> clonedSheet =
-        sheet->AsGecko()->Clone(nullptr, nullptr, nullptr, nullptr);
+        sheet->AsConcrete()->Clone(nullptr, nullptr, nullptr, nullptr);
       *aSheet = Move(clonedSheet);
       if (*aSheet && fromCompleteSheets &&
-          !sheet->AsGecko()->GetOwnerNode() &&
-          !sheet->AsGecko()->GetParentSheet()) {
+          !sheet->AsConcrete()->GetOwnerNode() &&
+          !sheet->AsConcrete()->GetParentSheet()) {
         // The sheet we're cloning isn't actually referenced by
         // anyone.  Replace it in the cache, so that if our CSSOM is
         // later modified we don't end up with two copies of our inner
         // hanging around.
         URIPrincipalReferrerPolicyAndCORSModeHashKey key(aURI, aLoaderPrincipal, aCORSMode, aReferrerPolicy);
-        NS_ASSERTION((*aSheet)->AsGecko()->IsComplete(),
+        NS_ASSERTION((*aSheet)->AsConcrete()->IsComplete(),
                      "Should only be caching complete sheets");
         mSheets->mCompleteSheets.Put(&key, *aSheet);
       }
@@ -1270,7 +1270,7 @@ Loader::PrepareSheet(StyleSheet* aSheet,
 {
   NS_PRECONDITION(aSheet, "Must have a sheet!");
 
-  CSSStyleSheet* sheet = aSheet->AsGecko();
+  CSSStyleSheet* sheet = aSheet->AsConcrete();
 
   RefPtr<nsMediaList> mediaList(aMediaList);
 
@@ -1397,10 +1397,10 @@ Loader::InsertChildSheet(StyleSheet* aSheet,
 
   // child sheets should always start out enabled, even if they got
   // cloned off of top-level sheets which were disabled
-  aSheet->AsGecko()->SetEnabled(true);
+  aSheet->AsConcrete()->SetEnabled(true);
 
   aParentSheet->AppendStyleSheet(aSheet);
-  aParentRule->SetSheet(aSheet->AsGecko()); // This sets the ownerRule on the sheet
+  aParentRule->SetSheet(aSheet->AsConcrete()); // This sets the ownerRule on the sheet
 
   LOG(("  Inserting into parent sheet"));
   //  LOG(("  Inserting into parent sheet at position %d", insertionPoint));
@@ -1741,7 +1741,7 @@ Loader::ParseSheet(const nsAString& aInput,
 
   nsresult rv;
 
-  nsCSSParser parser(this, aLoadData->mSheet->AsGecko());
+  nsCSSParser parser(this, aLoadData->mSheet->AsConcrete());
   rv = parser.ParseSheet(aInput, sheetURI, baseURI,
                          aLoadData->mSheet->Principal(),
                          aLoadData->mLineNumber);
@@ -1857,7 +1857,7 @@ Loader::DoSheetComplete(SheetLoadData* aLoadData, nsresult aStatus,
       // If mSheetAlreadyComplete, then the sheet could well be modified between
       // when we posted the async call to SheetComplete and now, since the sheet
       // was page-accessible during that whole time.
-      MOZ_ASSERT(!data->mSheet->AsGecko()->IsModified(),
+      MOZ_ASSERT(!data->mSheet->AsConcrete()->IsModified(),
                  "should not get marked modified during parsing");
       data->mSheet->SetComplete();
       data->ScheduleLoadEventIfNeeded(aStatus);
@@ -1899,10 +1899,10 @@ Loader::DoSheetComplete(SheetLoadData* aLoadData, nsresult aStatus,
     // parent sheet anyway, so that if someone then accesses it via
     // CSSOM we won't have extra clones of the inner lying around.
     data = aLoadData;
-    CSSStyleSheet* sheet = aLoadData->mSheet->AsGecko();
+    CSSStyleSheet* sheet = aLoadData->mSheet->AsConcrete();
     while (data) {
       if (data->mSheet->GetParentSheet() || data->mSheet->GetOwnerNode()) {
-        sheet = data->mSheet->AsGecko();
+        sheet = data->mSheet->AsConcrete();
         break;
       }
       data = data->mNext;
@@ -2216,7 +2216,7 @@ Loader::LoadChildSheet(StyleSheet* aParentSheet,
     LOG(("  No parent load; must be CSSOM"));
     // No parent load data, so the sheet will need to be notified when
     // we finish, if it can be, if we do the load asynchronously.
-    observer = aParentSheet->AsGecko();
+    observer = aParentSheet->AsConcrete();
   }
 
   // Now that we know it's safe to load this (passes security check and not a
@@ -2583,7 +2583,7 @@ NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(Loader)
          !iter.Done();
          iter.Next()) {
       NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(cb, "Sheet cache nsCSSLoader");
-      CSSStyleSheet* sheet = iter.UserData()->AsGecko();
+      CSSStyleSheet* sheet = iter.UserData()->AsConcrete();
       cb.NoteXPCOMChild(NS_ISUPPORTS_CAST(nsIDOMCSSStyleSheet*, sheet));
     }
   }
diff --git a/layout/style/StyleSheet.cpp b/layout/style/StyleSheet.cpp
index fcf23b8559..adcd0fc01b 100644
--- a/layout/style/StyleSheet.cpp
+++ b/layout/style/StyleSheet.cpp
@@ -79,7 +79,7 @@ StyleSheet::IsComplete() const
 void
 StyleSheet::SetComplete()
 {
-  NS_ASSERTION(!AsGecko()->mDirty,
+  NS_ASSERTION(!AsConcrete()->mDirty,
                "Can't set a dirty sheet complete!");
   SheetInfo().mComplete = true;
   if (mDocument && !mDisabled) {
@@ -135,7 +135,7 @@ StyleSheet::SetDisabled(bool aDisabled)
 {
   // DOM method, so handle BeginUpdate/EndUpdate
   MOZ_AUTO_DOC_UPDATE(mDocument, UPDATE_STYLE, true);
-  AsGecko()->SetEnabled(!aDisabled);
+  AsConcrete()->SetEnabled(!aDisabled);
   return NS_OK;
 }
 
@@ -229,7 +229,7 @@ StyleSheet::GetCssRules(nsIPrincipal& aSubjectPrincipal,
   if (!AreRulesAvailable(aSubjectPrincipal, aRv)) {
     return nullptr;
   }
-  return AsGecko()->GetCssRulesInternal(aRv);
+  return AsConcrete()->GetCssRulesInternal(aRv);
 }
 
 uint32_t
@@ -240,7 +240,7 @@ StyleSheet::InsertRule(const nsAString& aRule, uint32_t aIndex,
   if (!AreRulesAvailable(aSubjectPrincipal, aRv)) {
     return 0;
   }
-  return AsGecko()->InsertRuleInternal(aRule, aIndex, aRv);
+  return AsConcrete()->InsertRuleInternal(aRule, aIndex, aRv);
 }
 
 void
@@ -251,7 +251,7 @@ StyleSheet::DeleteRule(uint32_t aIndex,
   if (!AreRulesAvailable(aSubjectPrincipal, aRv)) {
     return;
   }
-  AsGecko()->DeleteRuleInternal(aIndex, aRv);
+  AsConcrete()->DeleteRuleInternal(aIndex, aRv);
 }
 
 int32_t
@@ -275,7 +275,7 @@ StyleSheet::AddRule(const nsAString& aSelector, const nsAString& aBlock,
   auto index =
       aIndex.WasPassed() ? aIndex.Value() : GetCssRules(aSubjectPrincipal, aRv)->Length();
 
-  return AsGecko()->InsertRuleInternal(rule, index, aRv);
+  return AsConcrete()->InsertRuleInternal(rule, index, aRv);
   // As per Microsoft documentation, always return -1.
   return -1;
 }
diff --git a/layout/style/StyleSheet.h b/layout/style/StyleSheet.h
index cf03b510e6..bbd455a02b 100644
--- a/layout/style/StyleSheet.h
+++ b/layout/style/StyleSheet.h
@@ -10,7 +10,6 @@
 #include "mozilla/dom/CSSStyleSheetBinding.h"
 #include "mozilla/net/ReferrerPolicy.h"
 #include "mozilla/CORSMode.h"
-#include "mozilla/DeprecatedUtils.h"
 
 #include "nsIDOMCSSStyleSheet.h"
 #include "nsWrapperCache.h"
@@ -64,7 +63,8 @@ public:
   bool IsComplete() const;
   void SetComplete();
 
-  MOZ_DECL_DEPRECATED_METHODS(CSSStyleSheet)
+  inline CSSStyleSheet* AsConcrete();
+  inline const CSSStyleSheet* AsConcrete() const;
 
   // Whether the sheet is for an inline <style> element.
   inline bool IsInline() const;
diff --git a/layout/style/StyleSheetInlines.h b/layout/style/StyleSheetInlines.h
index fd629f222b..5a73db2a97 100644
--- a/layout/style/StyleSheetInlines.h
+++ b/layout/style/StyleSheetInlines.h
@@ -11,18 +11,28 @@
 
 namespace mozilla {
 
-MOZ_DEFINE_DEPRECATED_METHODS(StyleSheet, CSSStyleSheet)
+CSSStyleSheet*
+StyleSheet::AsConcrete()
+{
+  return static_cast<CSSStyleSheet*>(this);
+}
+
+const CSSStyleSheet*
+StyleSheet::AsConcrete() const
+{
+  return static_cast<const CSSStyleSheet*>(this);
+}
 
 StyleSheetInfo&
 StyleSheet::SheetInfo()
 {
-  return *AsGecko()->mInner;
+  return *AsConcrete()->mInner;
 }
 
 const StyleSheetInfo&
 StyleSheet::SheetInfo() const
 {
-  return *AsGecko()->mInner;
+  return *AsConcrete()->mInner;
 }
 
 bool
@@ -71,7 +81,7 @@ StyleSheet::IsApplicable() const
 bool
 StyleSheet::HasRules() const
 {
-  return AsGecko()->HasRules();
+  return AsConcrete()->HasRules();
 }
 
 void
@@ -79,19 +89,19 @@ StyleSheet::SetAssociatedDocument(nsIDocument* aDocument,
                                   DocumentAssociationMode aAssociationMode)
 {
   MOZ_ASSERT(aDocument);
-  AsGecko()->SetAssociatedDocument(aDocument, aAssociationMode);
+  AsConcrete()->SetAssociatedDocument(aDocument, aAssociationMode);
 }
 
 void
 StyleSheet::ClearAssociatedDocument()
 {
-  AsGecko()->SetAssociatedDocument(nullptr, NotOwnedByDocument);
+  AsConcrete()->SetAssociatedDocument(nullptr, NotOwnedByDocument);
 }
 
 StyleSheet*
 StyleSheet::GetParentSheet() const
 {
-  return AsGecko()->GetParentSheet();
+  return AsConcrete()->GetParentSheet();
 }
 
 StyleSheet*
@@ -112,7 +122,7 @@ StyleSheet::GetParentObject() const
 void
 StyleSheet::AppendStyleSheet(StyleSheet* aSheet)
 {
-  AsGecko()->AppendStyleSheet(aSheet->AsGecko());
+  AsConcrete()->AppendStyleSheet(aSheet->AsConcrete());
 }
 
 nsIPrincipal*
@@ -155,19 +165,19 @@ StyleSheet::GetIntegrity(dom::SRIMetadata& aResult) const
 size_t
 StyleSheet::SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const
 {
-  return AsGecko()->SizeOfIncludingThis(aMallocSizeOf);
+  return AsConcrete()->SizeOfIncludingThis(aMallocSizeOf);
 }
 
 #ifdef DEBUG
 void
 StyleSheet::List(FILE* aOut, int32_t aIndex) const
 {
-  AsGecko()->List(aOut, aIndex);
+  AsConcrete()->List(aOut, aIndex);
 }
 #endif
 
-void StyleSheet::WillDirty() { AsGecko()->WillDirty(); }
-void StyleSheet::DidDirty() { AsGecko()->DidDirty(); }
+void StyleSheet::WillDirty() { AsConcrete()->WillDirty(); }
+void StyleSheet::DidDirty() { AsConcrete()->DidDirty(); }
 
 
 }
diff --git a/layout/style/moz.build b/layout/style/moz.build
index 680fcfc04f..7239526aa8 100644
--- a/layout/style/moz.build
+++ b/layout/style/moz.build
@@ -79,7 +79,6 @@ EXPORTS.mozilla += [
     'CSSVariableDeclarations.h',
     'CSSVariableResolver.h',
     'CSSVariableValues.h',
-    'DeprecatedUtils.h',
     'IncrementalClearCOMRuleArray.h',
     'LayerAnimationInfo.h',
     'RuleNodeCacheConditions.h',
diff --git a/layout/style/nsLayoutStylesheetCache.cpp b/layout/style/nsLayoutStylesheetCache.cpp
index 3072e4f201..4f83233868 100644
--- a/layout/style/nsLayoutStylesheetCache.cpp
+++ b/layout/style/nsLayoutStylesheetCache.cpp
@@ -491,7 +491,6 @@ nsLayoutStylesheetCache::InvalidateSheet(RefPtr<StyleSheet>* aSheet)
 {
   MOZ_ASSERT(gCSSLoader, "pref changed before we loaded a sheet?");
 
-  // TODO: this redundant check goes away once we get rid of AsGecko.
   const bool hasSheet = aSheet && *aSheet;
   if (hasSheet && gCSSLoader) {
     nsIURI* uri = (*aSheet)->GetSheetURI();
@@ -628,7 +627,7 @@ nsLayoutStylesheetCache::BuildPreferenceSheet(RefPtr<StyleSheet>* aSheet,
                "kPreallocSize should be big enough to build preference style "
                "sheet without reallocation");
 
-  sheet->AsGecko()->ReparseSheet(sheetText);
+  sheet->AsConcrete()->ReparseSheet(sheetText);
 
 #undef NS_GET_R_G_B
 }
diff --git a/layout/style/nsStyleSet.cpp b/layout/style/nsStyleSet.cpp
index a27dccc4b8..8c0a20471a 100644
--- a/layout/style/nsStyleSet.cpp
+++ b/layout/style/nsStyleSet.cpp
@@ -750,7 +750,7 @@ nsStyleSet::AppendAllXBLStyleSheets(nsTArray<mozilla::CSSStyleSheet*>& aArray) c
     AutoTArray<StyleSheet*, 32> sheets;
     mBindingManager->AppendAllSheets(sheets);
     for (StyleSheet* handle : sheets) {
-      aArray.AppendElement(handle->AsGecko());
+      aArray.AppendElement(handle->AsConcrete());
     }
   }
 }
@@ -2466,7 +2466,7 @@ nsStyleSet::EnsureUniqueInnerOnCSSSheets()
     AutoTArray<StyleSheet*, 32> sheets;
     mBindingManager->AppendAllSheets(sheets);
     for (StyleSheet* sheet : sheets) {
-      queue.AppendElement(sheet->AsGecko());
+      queue.AppendElement(sheet->AsConcrete());
     }
   }