diff --git a/dom/animation/KeyframeUtils.cpp b/dom/animation/KeyframeUtils.cpp
index 59f05652a..a3702dbe4 100644
--- a/dom/animation/KeyframeUtils.cpp
+++ b/dom/animation/KeyframeUtils.cpp
@@ -323,7 +323,7 @@ public:
 // ------------------------------------------------------------------
 
 inline bool
-IsInvalidValuePair(const PropertyValuePair& aPair, StyleBackendType aBackend)
+IsInvalidValuePair(const PropertyValuePair& aPair)
 {
   // There are three types of values we store as token streams:
   //
@@ -595,8 +595,6 @@ KeyframeUtils::GetComputedKeyframeValues(const nsTArray<Keyframe>& aKeyframes,
   MOZ_ASSERT(aStyleContext);
   MOZ_ASSERT(aElement);
 
-  StyleBackendType styleBackend = aElement->OwnerDoc()->GetStyleBackendType();
-
   const size_t len = aKeyframes.Length();
   nsTArray<ComputedKeyframeValues> result(len);
 
@@ -605,7 +603,7 @@ KeyframeUtils::GetComputedKeyframeValues(const nsTArray<Keyframe>& aKeyframes,
     ComputedKeyframeValues* computedValues = result.AppendElement();
     for (const PropertyValuePair& pair :
            PropertyPriorityIterator(frame.mPropertyValues)) {
-      if (IsInvalidValuePair(pair, styleBackend)) {
+      if (IsInvalidValuePair(pair)) {
         continue;
       }
 
@@ -1496,8 +1494,6 @@ HasImplicitKeyframeValues(const nsTArray<Keyframe>& aKeyframes,
     }
   };
 
-  StyleBackendType styleBackend = aDocument->GetStyleBackendType();
-
   for (size_t i = 0, len = aKeyframes.Length(); i < len; i++) {
     const Keyframe& frame = aKeyframes[i];
 
@@ -1513,7 +1509,7 @@ HasImplicitKeyframeValues(const nsTArray<Keyframe>& aKeyframes,
                          : computedOffset;
 
     for (const PropertyValuePair& pair : frame.mPropertyValues) {
-      if (IsInvalidValuePair(pair, styleBackend)) {
+      if (IsInvalidValuePair(pair)) {
         continue;
       }
 
diff --git a/dom/base/nsDOMWindowUtils.cpp b/dom/base/nsDOMWindowUtils.cpp
index 68f07deb8..cb1d588e2 100644
--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -3394,7 +3394,7 @@ nsDOMWindowUtils::AddSheet(nsIPreloadedStyleSheet* aSheet, uint32_t aSheetType)
 
   StyleSheet* sheet = nullptr;
   auto preloadedSheet = static_cast<PreloadedStyleSheet*>(aSheet);
-  nsresult rv = preloadedSheet->GetSheet(doc->GetStyleBackendType(), &sheet);
+  nsresult rv = preloadedSheet->GetSheet(&sheet);
   NS_ENSURE_SUCCESS(rv, rv);
   NS_ENSURE_TRUE(sheet, NS_ERROR_FAILURE);
 
diff --git a/dom/base/nsDocument.cpp b/dom/base/nsDocument.cpp
index ea702105f..91660017b 100644
--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -2171,8 +2171,7 @@ nsDocument::ResetStylesheetsToURI(nsIURI* aURI)
   mozAutoDocUpdate upd(this, UPDATE_STYLE, true);
   if (mStyleSetFilled) {
     // Skip removing style sheets from the style set if we know we haven't
-    // filled the style set.  (This allows us to avoid calling
-    // GetStyleBackendType() too early.)
+    // filled the style set.
     RemoveDocStyleSheetsFromStyleSets();
     RemoveStyleSheetsFromStyleSets(mOnDemandBuiltInUASheets, SheetType::Agent);
     RemoveStyleSheetsFromStyleSets(mAdditionalSheets[eAgentSheet], SheetType::Agent);
@@ -12568,16 +12567,6 @@ nsIDocument::ReportHasScrollLinkedEffect()
                                   "ScrollLinkedEffectFound2");
 }
 
-void
-nsIDocument::UpdateStyleBackendType()
-{
-  MOZ_ASSERT(mStyleBackendType == StyleBackendType(0),
-             "no need to call UpdateStyleBackendType now");
-
-  // Assume Gecko by default.
-  mStyleBackendType = StyleBackendType::Gecko;
-}
-
 /**
  * Helper function for |nsDocument::PrincipalFlashClassification|
  *
diff --git a/dom/base/nsIDocument.h b/dom/base/nsIDocument.h
index 77c349ead..f41000553 100644
--- a/dom/base/nsIDocument.h
+++ b/dom/base/nsIDocument.h
@@ -36,7 +36,6 @@
 #include "mozilla/dom/DocumentOrShadowRoot.h"
 #include "mozilla/dom/Dispatcher.h"
 #include "mozilla/LinkedList.h"
-#include "mozilla/StyleBackendType.h"
 #include "mozilla/StyleSheet.h"
 #include "mozilla/TimeStamp.h"
 #include "mozilla/UniquePtr.h"
@@ -1198,16 +1197,6 @@ public:
     return mCSSLoader;
   }
 
-  mozilla::StyleBackendType GetStyleBackendType() const {
-    if (mStyleBackendType == mozilla::StyleBackendType(0)) {
-      const_cast<nsIDocument*>(this)->UpdateStyleBackendType();
-    }
-    MOZ_ASSERT(mStyleBackendType != mozilla::StyleBackendType(0));
-    return mStyleBackendType;
-  }
-
-  void UpdateStyleBackendType();
-
   /**
    * Get this document's StyleImageLoader.  This is guaranteed to not return null.
    */
@@ -3252,10 +3241,6 @@ protected:
   // Our readyState
   ReadyState mReadyState;
 
-  // Whether this document has (or will have, once we have a pres shell) a
-  // Gecko- or Servo-backed style system.
-  mozilla::StyleBackendType mStyleBackendType;
-
 #ifdef MOZILLA_INTERNAL_API
   // Our visibility state
   mozilla::dom::VisibilityState mVisibilityState;
diff --git a/layout/base/PresShell.cpp b/layout/base/PresShell.cpp
index 2366059f2..a5cd94c08 100644
--- a/layout/base/PresShell.cpp
+++ b/layout/base/PresShell.cpp
@@ -36,7 +36,6 @@
 #include "mozilla/TouchEvents.h"
 #include "mozilla/UniquePtr.h"
 #include "mozilla/Unused.h"
-#include "mozilla/StyleBackendType.h"
 #include <algorithm>
 
 #ifdef XP_WIN
@@ -872,8 +871,7 @@ PresShell::Init(nsIDocument* aDocument,
 
   // Bind the context to the presentation shell.
   mPresContext = aPresContext;
-  StyleBackendType backend = StyleBackendType::Gecko;
-  aPresContext->AttachShell(this, backend);
+  aPresContext->AttachShell(this);
 
   // Now we can initialize the style set. Make sure to set the member before
   // calling Init, since various subroutines need to find the style set off
diff --git a/layout/base/RestyleManagerHandle.h b/layout/base/RestyleManagerHandle.h
index 813dab3ad..2d774faab 100644
--- a/layout/base/RestyleManagerHandle.h
+++ b/layout/base/RestyleManagerHandle.h
@@ -11,7 +11,6 @@
 #include "mozilla/EventStates.h"
 #include "mozilla/HandleRefPtr.h"
 #include "mozilla/RefCountType.h"
-#include "mozilla/StyleBackendType.h"
 #include "nsChangeHint.h"
 
 namespace mozilla {
@@ -50,11 +49,6 @@ public:
   public:
     friend class ::mozilla::RestyleManagerHandle;
 
-    StyleBackendType BackendType() const
-    {
-      return StyleBackendType::Gecko;
-    }
-
     RestyleManager* AsGecko()
     {
       return reinterpret_cast<RestyleManager*>(mValue);
diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index b7da7f9da..1f3210c39 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -9137,14 +9137,6 @@ nsLayoutUtils::GetCumulativeApzCallbackTransform(nsIFrame* aFrame)
   return delta;
 }
 
-/* static */ bool
-nsLayoutUtils::SupportsServoStyleBackend(nsIDocument* aDocument)
-{
-  return StyloEnabled() &&
-         aDocument->IsHTMLOrXHTML() &&
-         static_cast<nsDocument*>(aDocument)->IsContentDocument();
-}
-
 static
 bool
 LineHasNonEmptyContentWorker(nsIFrame* aFrame)
diff --git a/layout/base/nsLayoutUtils.h b/layout/base/nsLayoutUtils.h
index ac889c47c..f0de05d82 100644
--- a/layout/base/nsLayoutUtils.h
+++ b/layout/base/nsLayoutUtils.h
@@ -2394,13 +2394,6 @@ public:
     return sTextCombineUprightDigitsEnabled;
   }
 
-  // Stylo (the Servo backend for Gecko's style system) is generally enabled
-  // or disabled at compile-time. However, we provide the additional capability
-  // to disable it dynamically in stylo-enabled builds via a pref.
-  static bool StyloEnabled() {
-    return false;
-  }
-
   static uint32_t IdlePeriodDeadlineLimit() {
     return sIdlePeriodDeadlineLimit;
   }
@@ -2828,14 +2821,6 @@ public:
    */
   static CSSPoint GetCumulativeApzCallbackTransform(nsIFrame* aFrame);
 
-  /*
-   * Returns whether the given document supports being rendered with a
-   * Servo-backed style system.  This checks whether Stylo is enabled
-   * globally, that the document is an HTML document, and that it is
-   * being presented in a content docshell.
-   */
-  static bool SupportsServoStyleBackend(nsIDocument* aDocument);
-
   /*
    * Checks whether a node is an invisible break.
    * If not, returns the first frame on the next line if such a next line exists.
diff --git a/layout/base/nsPresContext.cpp b/layout/base/nsPresContext.cpp
index f9f74015a..491fbafdf 100644
--- a/layout/base/nsPresContext.cpp
+++ b/layout/base/nsPresContext.cpp
@@ -889,7 +889,7 @@ nsPresContext::Init(nsDeviceContext* aDeviceContext)
 // Note: We don't hold a reference on the shell; it has a reference to
 // us
 void
-nsPresContext::AttachShell(nsIPresShell* aShell, StyleBackendType aBackendType)
+nsPresContext::AttachShell(nsIPresShell* aShell)
 {
   MOZ_ASSERT(!mShell);
   mShell = aShell;
diff --git a/layout/base/nsPresContext.h b/layout/base/nsPresContext.h
index e21342109..9d5f16371 100644
--- a/layout/base/nsPresContext.h
+++ b/layout/base/nsPresContext.h
@@ -42,7 +42,6 @@
 #include "mozilla/RestyleManagerHandle.h"
 #include "prenv.h"
 #include "mozilla/StaticPresData.h"
-#include "mozilla/StyleBackendType.h"
 
 class nsAString;
 class nsIPrintSettings;
@@ -166,7 +165,7 @@ public:
    * Set and detach presentation shell that this context is bound to.
    * A presentation context may only be bound to a single shell.
    */
-  void AttachShell(nsIPresShell* aShell, mozilla::StyleBackendType aBackendType);
+  void AttachShell(nsIPresShell* aShell);
   void DetachShell();
 
 
diff --git a/layout/style/CSS.cpp b/layout/style/CSS.cpp
index 1078945ee..49ea6ee59 100644
--- a/layout/style/CSS.cpp
+++ b/layout/style/CSS.cpp
@@ -24,7 +24,6 @@ struct SupportsParsingInfo
   nsIURI* mDocURI;
   nsIURI* mBaseURI;
   nsIPrincipal* mPrincipal;
-  StyleBackendType mStyleBackendType;
 };
 
 static nsresult
@@ -44,7 +43,6 @@ GetParsingInfo(const GlobalObject& aGlobal,
   aInfo.mDocURI = nsCOMPtr<nsIURI>(doc->GetDocumentURI()).get();
   aInfo.mBaseURI = nsCOMPtr<nsIURI>(doc->GetBaseURI()).get();
   aInfo.mPrincipal = win->GetPrincipal();
-  aInfo.mStyleBackendType = doc->GetStyleBackendType();
   return NS_OK;
 }
 
diff --git a/layout/style/CSSStyleSheet.cpp b/layout/style/CSSStyleSheet.cpp
index 18ab53890..825e39dd9 100644
--- a/layout/style/CSSStyleSheet.cpp
+++ b/layout/style/CSSStyleSheet.cpp
@@ -369,7 +369,7 @@ CSSStyleSheetInner::SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const
 
 CSSStyleSheet::CSSStyleSheet(css::SheetParsingMode aParsingMode,
                              CORSMode aCORSMode, ReferrerPolicy aReferrerPolicy)
-  : StyleSheet(StyleBackendType::Gecko, aParsingMode),
+  : StyleSheet(aParsingMode),
     mParent(nullptr),
     mOwnerRule(nullptr),
     mDirty(false),
@@ -385,7 +385,7 @@ CSSStyleSheet::CSSStyleSheet(css::SheetParsingMode aParsingMode,
                              CORSMode aCORSMode,
                              ReferrerPolicy aReferrerPolicy,
                              const SRIMetadata& aIntegrity)
-  : StyleSheet(StyleBackendType::Gecko, aParsingMode),
+  : StyleSheet(aParsingMode),
     mParent(nullptr),
     mOwnerRule(nullptr),
     mDirty(false),
diff --git a/layout/style/Declaration.h b/layout/style/Declaration.h
index f149a09b1..62cc02f14 100644
--- a/layout/style/Declaration.h
+++ b/layout/style/Declaration.h
@@ -92,7 +92,7 @@ public:
    * |mData|) and cannot be used until its |CompressFrom| method or
    * |InitializeEmpty| method is called.
    */
-  Declaration() : DeclarationBlock(StyleBackendType::Gecko) {}
+  Declaration() : DeclarationBlock() {}
 
   Declaration(const Declaration& aCopy);
 
diff --git a/layout/style/DeclarationBlock.h b/layout/style/DeclarationBlock.h
index b7863150c..5ab2441aa 100644
--- a/layout/style/DeclarationBlock.h
+++ b/layout/style/DeclarationBlock.h
@@ -13,7 +13,6 @@
 #define mozilla_DeclarationBlock_h
 
 #include "mozilla/ServoUtils.h"
-#include "mozilla/StyleBackendType.h"
 
 #include "nsCSSPropertyID.h"
 
@@ -31,11 +30,11 @@ class Rule;
 class DeclarationBlock
 {
 protected:
-  explicit DeclarationBlock(StyleBackendType aType)
-    : mImmutable(false), mType(aType) { mContainer.mRaw = 0; }
+  explicit DeclarationBlock()
+    : mImmutable(false) { mContainer.mRaw = 0; }
 
   DeclarationBlock(const DeclarationBlock& aCopy)
-    : DeclarationBlock(aCopy.mType) {}
+    : DeclarationBlock() {}
 
 public:
   MOZ_DECL_STYLO_METHODS(css::Declaration)
@@ -137,8 +136,6 @@ private:
   // set when declaration put in the rule tree;
   // also by ToString (hence the 'mutable').
   mutable bool mImmutable;
-
-  const StyleBackendType mType;
 };
 
 } // namespace mozilla
diff --git a/layout/style/PreloadedStyleSheet.cpp b/layout/style/PreloadedStyleSheet.cpp
index 709d3d077..5740ce786 100644
--- a/layout/style/PreloadedStyleSheet.cpp
+++ b/layout/style/PreloadedStyleSheet.cpp
@@ -39,10 +39,8 @@ PreloadedStyleSheet::Create(nsIURI* aURI,
 
   RefPtr<PreloadedStyleSheet> preloadedSheet =
     new PreloadedStyleSheet(aURI, aParsingMode);
-  auto type = nsLayoutUtils::StyloEnabled() ? StyleBackendType::Servo
-                                            : StyleBackendType::Gecko;
   StyleSheet* sheet;
-  nsresult rv = preloadedSheet->GetSheet(type, &sheet);
+  nsresult rv = preloadedSheet->GetSheet(&sheet);
   NS_ENSURE_SUCCESS(rv, rv);
 
   preloadedSheet.forget(aResult);
@@ -57,23 +55,21 @@ NS_INTERFACE_MAP_END
 NS_IMPL_CYCLE_COLLECTING_ADDREF(PreloadedStyleSheet)
 NS_IMPL_CYCLE_COLLECTING_RELEASE(PreloadedStyleSheet)
 
-NS_IMPL_CYCLE_COLLECTION(PreloadedStyleSheet, mGecko, mServo)
+NS_IMPL_CYCLE_COLLECTION(PreloadedStyleSheet, mStyleSheet)
 
 nsresult
-PreloadedStyleSheet::GetSheet(StyleBackendType aType, StyleSheet** aResult)
+PreloadedStyleSheet::GetSheet(StyleSheet** aResult)
 {
   *aResult = nullptr;
 
-  RefPtr<StyleSheet>& sheet = mGecko;
-
-  if (!sheet) {
+  if (!mStyleSheet) {
     RefPtr<css::Loader> loader = new css::Loader();
-    nsresult rv = loader->LoadSheetSync(mURI, mParsingMode, true, &sheet);
+    nsresult rv = loader->LoadSheetSync(mURI, mParsingMode, true, &mStyleSheet);
     NS_ENSURE_SUCCESS(rv, rv);
     MOZ_ASSERT(sheet);
   }
 
-  *aResult = sheet;
+  *aResult = mStyleSheet;
   return NS_OK;
 }
 
diff --git a/layout/style/PreloadedStyleSheet.h b/layout/style/PreloadedStyleSheet.h
index 5e427a557..47f005b8a 100644
--- a/layout/style/PreloadedStyleSheet.h
+++ b/layout/style/PreloadedStyleSheet.h
@@ -27,7 +27,7 @@ public:
 
   // *aResult is not addrefed, since the PreloadedStyleSheet holds a strong
   // reference to the sheet.
-  nsresult GetSheet(StyleBackendType aType, StyleSheet** aResult);
+  nsresult GetSheet(StyleSheet** aResult);
 
 protected:
   virtual ~PreloadedStyleSheet() {}
@@ -35,8 +35,7 @@ protected:
 private:
   PreloadedStyleSheet(nsIURI* aURI, css::SheetParsingMode aParsingMode);
 
-  RefPtr<StyleSheet> mGecko;
-  RefPtr<StyleSheet> mServo;
+  RefPtr<StyleSheet> mStyleSheet;
 
   nsCOMPtr<nsIURI> mURI;
   css::SheetParsingMode mParsingMode;
diff --git a/layout/style/ServoDeclarationBlock.h b/layout/style/ServoDeclarationBlock.h
index 8f78b772c..2d0ce2574 100644
--- a/layout/style/ServoDeclarationBlock.h
+++ b/layout/style/ServoDeclarationBlock.h
@@ -16,7 +16,7 @@ class ServoDeclarationBlock final : public DeclarationBlock
 public:
   explicit ServoDeclarationBlock(
     already_AddRefed<RawServoDeclarationBlock> aRaw)
-    : DeclarationBlock(StyleBackendType::Servo), mRaw(aRaw) {}
+    : DeclarationBlock(), mRaw(aRaw) {}
 
   ServoDeclarationBlock()
     : ServoDeclarationBlock(Servo_DeclarationBlock_CreateEmpty().Consume()) {}
diff --git a/layout/style/ServoStyleSheet.cpp b/layout/style/ServoStyleSheet.cpp
index 674adebdc..ae303dc6b 100644
--- a/layout/style/ServoStyleSheet.cpp
+++ b/layout/style/ServoStyleSheet.cpp
@@ -7,7 +7,6 @@
 #include "mozilla/ServoStyleSheet.h"
 
 #include "mozilla/css/Rule.h"
-#include "mozilla/StyleBackendType.h"
 #include "mozilla/ServoBindings.h"
 #include "mozilla/ServoCSSRuleList.h"
 #include "mozilla/dom/CSSRuleList.h"
@@ -22,7 +21,7 @@ ServoStyleSheet::ServoStyleSheet(css::SheetParsingMode aParsingMode,
                                  CORSMode aCORSMode,
                                  net::ReferrerPolicy aReferrerPolicy,
                                  const dom::SRIMetadata& aIntegrity)
-  : StyleSheet(StyleBackendType::Servo, aParsingMode)
+  : StyleSheet(aParsingMode)
   , mSheetInfo(aCORSMode, aReferrerPolicy, aIntegrity)
 {
 }
diff --git a/layout/style/StyleBackendType.h b/layout/style/StyleBackendType.h
deleted file mode 100644
index f02b86213..000000000
--- a/layout/style/StyleBackendType.h
+++ /dev/null
@@ -1,23 +0,0 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
-/* 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/. */
-
-#ifndef mozilla_StyleBackendType_h
-#define mozilla_StyleBackendType_h
-
-namespace mozilla {
-
-/**
- * Enumeration that represents one of the two supported style system backends.
- */
-enum class StyleBackendType : uint8_t
-{
-  Gecko = 1,
-  Servo
-};
-
-} // namespace mozilla
-
-#endif // mozilla_StyleBackendType_h
diff --git a/layout/style/StyleSetHandle.h b/layout/style/StyleSetHandle.h
index a2580fa91..378fbd662 100644
--- a/layout/style/StyleSetHandle.h
+++ b/layout/style/StyleSetHandle.h
@@ -11,7 +11,6 @@
 #include "mozilla/RefPtr.h"
 #include "mozilla/ServoTypes.h"
 #include "mozilla/SheetType.h"
-#include "mozilla/StyleBackendType.h"
 #include "mozilla/StyleSheet.h"
 #include "nsChangeHint.h"
 #include "nsCSSPseudoElements.h"
@@ -48,11 +47,6 @@ public:
   public:
     friend class ::mozilla::StyleSetHandle;
 
-    StyleBackendType BackendType() const
-    {
-      return StyleBackendType::Gecko;
-    }
-
     nsStyleSet* AsGecko()
     {
       return reinterpret_cast<nsStyleSet*>(mValue);
diff --git a/layout/style/StyleSheet.cpp b/layout/style/StyleSheet.cpp
index c55c40d69..f2ed540a0 100644
--- a/layout/style/StyleSheet.cpp
+++ b/layout/style/StyleSheet.cpp
@@ -18,11 +18,10 @@
 
 namespace mozilla {
 
-StyleSheet::StyleSheet(StyleBackendType aType, css::SheetParsingMode aParsingMode)
+StyleSheet::StyleSheet(css::SheetParsingMode aParsingMode)
   : mDocument(nullptr)
   , mOwningNode(nullptr)
   , mParsingMode(aParsingMode)
-  , mType(aType)
   , mDisabled(false)
   , mDocumentAssociationMode(NotOwnedByDocument)
 {
@@ -35,7 +34,6 @@ StyleSheet::StyleSheet(const StyleSheet& aCopy,
   , mDocument(aDocumentToUse)
   , mOwningNode(aOwningNodeToUse)
   , mParsingMode(aCopy.mParsingMode)
-  , mType(aCopy.mType)
   , mDisabled(aCopy.mDisabled)
     // We only use this constructor during cloning.  It's the cloner's
     // responsibility to notify us if we end up being owned by a document.
diff --git a/layout/style/StyleSheet.h b/layout/style/StyleSheet.h
index 5472143bb..853439df1 100644
--- a/layout/style/StyleSheet.h
+++ b/layout/style/StyleSheet.h
@@ -10,7 +10,6 @@
 #include "mozilla/css/SheetParsingMode.h"
 #include "mozilla/dom/CSSStyleSheetBinding.h"
 #include "mozilla/net/ReferrerPolicy.h"
-#include "mozilla/StyleBackendType.h"
 #include "mozilla/CORSMode.h"
 #include "mozilla/ServoUtils.h"
 
@@ -44,7 +43,7 @@ class StyleSheet : public nsIDOMCSSStyleSheet
                  , public nsWrapperCache
 {
 protected:
-  StyleSheet(StyleBackendType aType, css::SheetParsingMode aParsingMode);
+  StyleSheet(css::SheetParsingMode aParsingMode);
   StyleSheet(const StyleSheet& aCopy,
              nsIDocument* aDocumentToUse,
              nsINode* aOwningNodeToUse);
@@ -245,7 +244,6 @@ protected:
   // and/or useful in user sheets.
   css::SheetParsingMode mParsingMode;
 
-  const StyleBackendType mType;
   bool                  mDisabled;
 
   // mDocumentAssociationMode determines whether mDocument directly owns us (in
diff --git a/layout/style/moz.build b/layout/style/moz.build
index 6f6037ad4..abe7bd00c 100644
--- a/layout/style/moz.build
+++ b/layout/style/moz.build
@@ -107,7 +107,6 @@ EXPORTS.mozilla += [
     'ServoUtils.h',
     'SheetType.h',
     'StyleAnimationValue.h',
-    'StyleBackendType.h',
     'StyleComplexColor.h',
     'StyleContextSource.h',
     'StyleSetHandle.h',