--- a/layout/style/ServoKeyframeRule.cpp
+++ b/layout/style/ServoKeyframeRule.cpp
@@ -52,23 +52,16 @@ public:
         mDecls->SetOwningRule(nullptr);
         mDecls = aDecls->AsServo();
         mDecls->SetOwningRule(mRule);
         Servo_Keyframe_SetStyle(mRule->Raw(), mDecls->Raw());
       }
     });
     return NS_OK;
   }
-  void GetCSSParsingEnvironment(CSSParsingEnvironment& aCSSParseEnv,
-                                nsIPrincipal* aSubjectPrincipal) final
-  {
-    MOZ_ASSERT_UNREACHABLE("GetCSSParsingEnvironment "
-                           "shouldn't be calling for a Servo rule");
-    GetCSSParsingEnvironmentForRule(mRule, aCSSParseEnv);
-  }
   ServoCSSParsingEnvironment GetServoCSSParsingEnvironment(
       nsIPrincipal* aSubjectPrincipal) const final
   {
     return GetServoCSSParsingEnvironmentForRule(mRule);
   }
   nsIDocument* DocToUpdate() final { return nullptr; }
 
   nsINode* GetParentObject() final

--- a/layout/style/ServoPageRule.cpp
+++ b/layout/style/ServoPageRule.cpp
@@ -82,26 +82,16 @@ ServoPageRuleDeclaration::SetCSSDeclarat
 }
 
 nsIDocument*
 ServoPageRuleDeclaration::DocToUpdate()
 {
   return nullptr;
 }
 
-void
-ServoPageRuleDeclaration::GetCSSParsingEnvironment(
-  CSSParsingEnvironment& aCSSParseEnv,
-  nsIPrincipal* aSubjectPrincipal)
-{
-  MOZ_ASSERT_UNREACHABLE("GetCSSParsingEnvironment "
-                         "shouldn't be calling for a Servo rule");
-  GetCSSParsingEnvironmentForRule(Rule(), aCSSParseEnv);
-}
-
 nsDOMCSSDeclaration::ServoCSSParsingEnvironment
 ServoPageRuleDeclaration::GetServoCSSParsingEnvironment(
   nsIPrincipal* aSubjectPrincipal) const
 {
   return GetServoCSSParsingEnvironmentForRule(Rule());
 }
 
 // -- ServoPageRule --------------------------------------------------

--- a/layout/style/ServoPageRule.h
+++ b/layout/style/ServoPageRule.h
@@ -30,18 +30,16 @@ public:
 
   css::Rule* GetParentRule() final;
   nsINode* GetParentObject() final;
 
 protected:
   DeclarationBlock* GetCSSDeclaration(Operation aOperation) final;
   nsresult SetCSSDeclaration(DeclarationBlock* aDecl) final;
   nsIDocument* DocToUpdate() final;
-  void GetCSSParsingEnvironment(CSSParsingEnvironment& aCSSParseEnv,
-                                nsIPrincipal* aSubjectPrincipal) final;
   nsDOMCSSDeclaration::ServoCSSParsingEnvironment
   GetServoCSSParsingEnvironment(nsIPrincipal* aSubjectPrincipal) const final;
 
 private:
   // For accessing the constructor.
   friend class ServoPageRule;
 
   explicit ServoPageRuleDeclaration(

--- a/layout/style/ServoStyleRule.cpp
+++ b/layout/style/ServoStyleRule.cpp
@@ -87,26 +87,16 @@ ServoStyleRuleDeclaration::SetCSSDeclara
 }
 
 nsIDocument*
 ServoStyleRuleDeclaration::DocToUpdate()
 {
   return nullptr;
 }
 
-void
-ServoStyleRuleDeclaration::GetCSSParsingEnvironment(
-  CSSParsingEnvironment& aCSSParseEnv,
-  nsIPrincipal* aSubjectPrincipal)
-{
-  MOZ_ASSERT_UNREACHABLE("GetCSSParsingEnvironment "
-                         "shouldn't be calling for a Servo rule");
-  GetCSSParsingEnvironmentForRule(Rule(), aCSSParseEnv);
-}
-
 nsDOMCSSDeclaration::ServoCSSParsingEnvironment
 ServoStyleRuleDeclaration::GetServoCSSParsingEnvironment(
   nsIPrincipal* aSubjectPrincipal) const
 {
   return GetServoCSSParsingEnvironmentForRule(Rule());
 }
 
 // -- ServoStyleRule --------------------------------------------------

--- a/layout/style/ServoStyleRule.h
+++ b/layout/style/ServoStyleRule.h
@@ -31,18 +31,16 @@ public:
 
   css::Rule* GetParentRule() final;
   nsINode* GetParentObject() final;
 
 protected:
   DeclarationBlock* GetCSSDeclaration(Operation aOperation) final;
   nsresult SetCSSDeclaration(DeclarationBlock* aDecl) final;
   nsIDocument* DocToUpdate() final;
-  void GetCSSParsingEnvironment(CSSParsingEnvironment& aCSSParseEnv,
-                                nsIPrincipal* aSubjectPrincipal) final;
   ServoCSSParsingEnvironment
   GetServoCSSParsingEnvironment(nsIPrincipal* aSubjectPrincipal) const final;
 
 private:
   // For accessing the constructor.
   friend class ServoStyleRule;
 
   explicit ServoStyleRuleDeclaration(

--- a/layout/style/nsComputedDOMStyle.cpp
+++ b/layout/style/nsComputedDOMStyle.cpp
@@ -753,23 +753,16 @@ nsComputedDOMStyle::SetCSSDeclaration(De
 }
 
 nsIDocument*
 nsComputedDOMStyle::DocToUpdate()
 {
   MOZ_CRASH("called nsComputedDOMStyle::DocToUpdate");
 }
 
-void
-nsComputedDOMStyle::GetCSSParsingEnvironment(CSSParsingEnvironment& aCSSParseEnv,
-                                             nsIPrincipal* aSubjectPrincipal)
-{
-  MOZ_CRASH("called nsComputedDOMStyle::GetCSSParsingEnvironment");
-}
-
 nsDOMCSSDeclaration::ServoCSSParsingEnvironment
 nsComputedDOMStyle::GetServoCSSParsingEnvironment(
   nsIPrincipal* aSubjectPrincipal) const
 {
   MOZ_CRASH("called nsComputedDOMStyle::GetServoCSSParsingEnvironment");
 }
 
 void

--- a/layout/style/nsComputedDOMStyle.h
+++ b/layout/style/nsComputedDOMStyle.h
@@ -127,18 +127,17 @@ public:
                        mozilla::ErrorResult& aRv) final;
 
   // nsDOMCSSDeclaration abstract methods which should never be called
   // on a nsComputedDOMStyle object, but must be defined to avoid
   // compile errors.
   virtual mozilla::DeclarationBlock* GetCSSDeclaration(Operation) override;
   virtual nsresult SetCSSDeclaration(mozilla::DeclarationBlock*) override;
   virtual nsIDocument* DocToUpdate() override;
-  virtual void GetCSSParsingEnvironment(CSSParsingEnvironment& aCSSParseEnv,
-                                        nsIPrincipal* aSubjectPrincipal) override;
+
   nsDOMCSSDeclaration::ServoCSSParsingEnvironment
   GetServoCSSParsingEnvironment(nsIPrincipal* aSubjectPrincipal) const final;
 
   static already_AddRefed<nsROCSSPrimitiveValue>
     MatrixToCSSValue(const mozilla::gfx::Matrix4x4& aMatrix);
 
   static void RegisterPrefChangeCallbacks();
   static void UnregisterPrefChangeCallbacks();

--- a/layout/style/nsDOMCSSAttrDeclaration.cpp
+++ b/layout/style/nsDOMCSSAttrDeclaration.cpp
@@ -151,30 +151,16 @@ nsDOMCSSAttributeDeclaration::GetCSSDecl
 
   if (NS_FAILED(rv)) {
     return nullptr; // the decl will be destroyed along with the style rule
   }
 
   return decl;
 }
 
-void
-nsDOMCSSAttributeDeclaration::GetCSSParsingEnvironment(CSSParsingEnvironment& aCSSParseEnv,
-                                                       nsIPrincipal* aSubjectPrincipal)
-{
-  NS_ASSERTION(mElement, "Something is severely broken -- there should be an Element here!");
-
-  nsIDocument* doc = mElement->OwnerDoc();
-  aCSSParseEnv.mSheetURI = doc->GetDocumentURI();
-  aCSSParseEnv.mBaseURI = mElement->GetBaseURIForStyleAttr();
-  aCSSParseEnv.mPrincipal = (aSubjectPrincipal ? aSubjectPrincipal
-                                               : mElement->NodePrincipal());
-  aCSSParseEnv.mCSSLoader = doc->CSSLoader();
-}
-
 nsDOMCSSDeclaration::ServoCSSParsingEnvironment
 nsDOMCSSAttributeDeclaration::GetServoCSSParsingEnvironment(
     nsIPrincipal* aSubjectPrincipal) const
 {
   return {
     mElement->GetURLDataForStyleAttr(aSubjectPrincipal),
     mElement->OwnerDoc()->GetCompatibilityMode(),
     mElement->OwnerDoc()->CSSLoader(),

--- a/layout/style/nsDOMCSSAttrDeclaration.h
+++ b/layout/style/nsDOMCSSAttrDeclaration.h
@@ -29,21 +29,21 @@ public:
   nsDOMCSSAttributeDeclaration(Element* aContent, bool aIsSMILOverride);
 
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS
   NS_DECL_CYCLE_COLLECTION_SKIPPABLE_SCRIPT_HOLDER_CLASS_AMBIGUOUS(nsDOMCSSAttributeDeclaration,
                                                                    nsICSSDeclaration)
 
   // If GetCSSDeclaration returns non-null, then the decl it returns
   // is owned by our current style rule.
-  virtual mozilla::DeclarationBlock* GetCSSDeclaration(Operation aOperation) override;
-  virtual void GetCSSParsingEnvironment(CSSParsingEnvironment& aCSSParseEnv,
-                                        nsIPrincipal* aSubjectPrincipal) override;
+  mozilla::DeclarationBlock* GetCSSDeclaration(Operation aOperation) final;
+
   nsDOMCSSDeclaration::ServoCSSParsingEnvironment
-  GetServoCSSParsingEnvironment(nsIPrincipal* aSubjectPrincipal) const final;
+    GetServoCSSParsingEnvironment(nsIPrincipal* aSubjectPrincipal) const final;
+
   mozilla::css::Rule* GetParentRule() override
   {
     return nullptr;
   }
 
   nsINode* GetParentObject() override
   {
     return mElement;

--- a/layout/style/nsDOMCSSDeclaration.cpp
+++ b/layout/style/nsDOMCSSDeclaration.cpp
@@ -223,33 +223,16 @@ NS_IMETHODIMP
 nsDOMCSSDeclaration::RemoveProperty(const nsAString& aPropertyName,
                                     nsAString& aReturn)
 {
   nsresult rv = GetPropertyValue(aPropertyName, aReturn);
   NS_ENSURE_SUCCESS(rv, rv);
   return RemovePropertyInternal(aPropertyName);
 }
 
-/* static */ void
-nsDOMCSSDeclaration::GetCSSParsingEnvironmentForRule(css::Rule* aRule,
-                                                     CSSParsingEnvironment& aCSSParseEnv)
-{
-  StyleSheet* sheet = aRule ? aRule->GetStyleSheet() : nullptr;
-  if (!sheet) {
-    aCSSParseEnv.mPrincipal = nullptr;
-    return;
-  }
-
-  nsIDocument* document = sheet->GetAssociatedDocument();
-  aCSSParseEnv.mSheetURI = sheet->GetSheetURI();
-  aCSSParseEnv.mBaseURI = sheet->GetBaseURI();
-  aCSSParseEnv.mPrincipal = sheet->Principal();
-  aCSSParseEnv.mCSSLoader = document ? document->CSSLoader() : nullptr;
-}
-
 /* static */ nsDOMCSSDeclaration::ServoCSSParsingEnvironment
 nsDOMCSSDeclaration::GetServoCSSParsingEnvironmentForRule(const css::Rule* aRule)
 {
   StyleSheet* sheet = aRule ? aRule->GetStyleSheet() : nullptr;
   if (!sheet) {
     return { nullptr, eCompatibility_FullStandards, nullptr };
   }
 

--- a/layout/style/nsDOMCSSDeclaration.h
+++ b/layout/style/nsDOMCSSDeclaration.h
@@ -160,59 +160,26 @@ protected:
   };
   virtual mozilla::DeclarationBlock* GetCSSDeclaration(Operation aOperation) = 0;
   virtual nsresult SetCSSDeclaration(mozilla::DeclarationBlock* aDecl) = 0;
   // Document that we must call BeginUpdate/EndUpdate on around the
   // calls to SetCSSDeclaration and the style rule mutation that leads
   // to it.
   virtual nsIDocument* DocToUpdate() = 0;
 
-  // Information neded to parse a declaration.  We need the mSheetURI
-  // for error reporting, mBaseURI to resolve relative URIs,
-  // mPrincipal for subresource loads, and mCSSLoader for determining
-  // whether we're in quirks mode.  mBaseURI needs to be a strong
-  // pointer because of xml:base possibly creating base URIs on the
-  // fly.  This is why we don't use CSSParsingEnvironment as a return
-  // value, to avoid multiple-refcounting of mBaseURI.
-  struct CSSParsingEnvironment {
-    nsIURI* MOZ_UNSAFE_REF("user of CSSParsingEnviroment must hold an owning "
-                           "reference; reference counting here has unacceptable "
-                           "performance overhead (see bug 649163)") mSheetURI;
-    nsCOMPtr<nsIURI> mBaseURI;
-    nsIPrincipal* MOZ_UNSAFE_REF("user of CSSParsingEnviroment must hold an owning "
-                                 "reference; reference counting here has unacceptable "
-                                 "performance overhead (see bug 649163)") mPrincipal;
-    mozilla::css::Loader* MOZ_UNSAFE_REF("user of CSSParsingEnviroment must hold an owning "
-                                         "reference; reference counting here has unacceptable "
-                                         "performance overhead (see bug 649163)") mCSSLoader;
-  };
-
-  // On failure, mPrincipal should be set to null in aCSSParseEnv.
-  // If mPrincipal is null, the other members may not be set to
-  // anything meaningful.
-  // If aSubjectPrincipal is passed, it should be the subject principal of the
-  // scripted caller that initiated the parser.
-  virtual void GetCSSParsingEnvironment(CSSParsingEnvironment& aCSSParseEnv,
-                                        nsIPrincipal* aSubjectPrincipal = nullptr) = 0;
-
   // mUrlExtraData returns URL data for parsing url values in
   // CSS. Returns nullptr on failure. If mUrlExtraData is nullptr,
   // mCompatMode may not be set to anything meaningful.
   // If aSubjectPrincipal is passed, it should be the subject principal of the
   // scripted caller that initiated the parser.
   virtual ServoCSSParsingEnvironment
   GetServoCSSParsingEnvironment(nsIPrincipal* aSubjectPrincipal = nullptr) const = 0;
 
-  // An implementation for GetCSSParsingEnvironment for callers wrapping
-  // an css::Rule.
-  static void GetCSSParsingEnvironmentForRule(mozilla::css::Rule* aRule,
-                                              CSSParsingEnvironment& aCSSParseEnv);
-
-  // An implementation for GetServoCSSParsingEnvironment for callers wrapping
-  // an css::Rule.
+  // An implementation for GetServoCSSParsingEnvironment for callers wrapping a
+  // css::Rule.
   static ServoCSSParsingEnvironment
     GetServoCSSParsingEnvironmentForRule(const mozilla::css::Rule* aRule);
 
   nsresult ParsePropertyValue(const nsCSSPropertyID aPropID,
                               const nsAString& aPropValue,
                               bool aIsImportant,
                               nsIPrincipal* aSubjectPrincipal);