--- a/layout/style/CSSStyleSheet.cpp
+++ b/layout/style/CSSStyleSheet.cpp
@@ -1623,89 +1623,42 @@ CSSStyleSheet::RegisterNamespaceRule(css
     nsresult rv = mInner->CreateNamespaceMap();
     NS_ENSURE_SUCCESS(rv, rv);
   }
 
   AddNamespaceRuleToMap(aRule, mInner->mNameSpaceMap);
   return NS_OK;
 }
 
-  // nsIDOMStyleSheet interface
-
-NS_IMETHODIMP
-CSSStyleSheet::GetParentStyleSheet(nsIDOMStyleSheet** aParentStyleSheet)
-{
-  NS_ENSURE_ARG_POINTER(aParentStyleSheet);
-
-  NS_IF_ADDREF(*aParentStyleSheet = mParent);
-
-  return NS_OK;
-}
-
-NS_IMETHODIMP
-CSSStyleSheet::GetMedia(nsIDOMMediaList** aMedia)
-{
-  NS_ADDREF(*aMedia = Media());
-  return NS_OK;
-}
-
 nsMediaList*
 CSSStyleSheet::Media()
 {
   if (!mMedia) {
     mMedia = new nsMediaList();
     mMedia->SetStyleSheet(this);
   }
 
   return mMedia;
 }
 
-NS_IMETHODIMP    
-CSSStyleSheet::GetOwnerRule(nsIDOMCSSRule** aOwnerRule)
-{
-  NS_IF_ADDREF(*aOwnerRule = GetOwnerRule());
-  return NS_OK;
-}
-
 nsIDOMCSSRule*
 CSSStyleSheet::GetDOMOwnerRule() const
 {
   return mOwnerRule ? mOwnerRule->GetDOMRule() : nullptr;
 }
 
-NS_IMETHODIMP    
-CSSStyleSheet::GetCssRules(nsIDOMCSSRuleList** aCssRules)
-{
-  ErrorResult rv;
-  nsCOMPtr<nsIDOMCSSRuleList> rules =
-    GetCssRules(Some(nsContentUtils::SubjectPrincipal()), rv);
-  rules.forget(aCssRules);
-  return rv.StealNSResult();
-}
-
 CSSRuleList*
 CSSStyleSheet::GetCssRulesInternal(ErrorResult& aRv)
 {
   if (!mRuleCollection) {
     mRuleCollection = new CSSRuleListImpl(this);
   }
   return mRuleCollection;
 }
 
-NS_IMETHODIMP    
-CSSStyleSheet::InsertRule(const nsAString& aRule,
-                          uint32_t aIndex,
-                          uint32_t* aReturn)
-{
-  ErrorResult rv;
-  *aReturn =
-    InsertRule(aRule, aIndex, Some(nsContentUtils::SubjectPrincipal()), rv);
-  return rv.StealNSResult();
-}
-
 static bool
 RuleHasPendingChildSheet(css::Rule *cssRule)
 {
   nsCOMPtr<nsIDOMCSSImportRule> importRule(do_QueryInterface(cssRule));
   NS_ASSERTION(importRule, "Rule which has type IMPORT_RULE and does not implement nsIDOMCSSImportRule!");
   nsCOMPtr<nsIDOMCSSStyleSheet> childSheet;
   importRule->GetStyleSheet(getter_AddRefs(childSheet));
   RefPtr<CSSStyleSheet> cssSheet = do_QueryObject(childSheet);
@@ -1827,24 +1780,16 @@ CSSStyleSheet::InsertRuleInternal(const 
   if ((type != css::Rule::IMPORT_RULE || !RuleHasPendingChildSheet(rule)) &&
       mDocument) {
     mDocument->StyleRuleAdded(this, rule);
   }
 
   return aIndex;
 }
 
-NS_IMETHODIMP    
-CSSStyleSheet::DeleteRule(uint32_t aIndex)
-{
-  ErrorResult rv;
-  DeleteRule(aIndex, Some(nsContentUtils::SubjectPrincipal()), rv);
-  return rv.StealNSResult();
-}
-
 void
 CSSStyleSheet::DeleteRuleInternal(uint32_t aIndex, ErrorResult& aRv)
 {
   // XXX TBI: handle @rule types
   mozAutoDocUpdate updateBatch(mDocument, UPDATE_STYLE, true);
     
   WillDirty();
 

--- a/layout/style/CSSStyleSheet.h
+++ b/layout/style/CSSStyleSheet.h
@@ -157,16 +157,18 @@ public:
   nsresult DeleteRuleFromGroup(css::GroupRule* aGroup, uint32_t aIndex);
   nsresult InsertRuleIntoGroup(const nsAString& aRule, css::GroupRule* aGroup, uint32_t aIndex, uint32_t* _retval);
 
   void SetTitle(const nsAString& aTitle) { mTitle = aTitle; }
   void SetMedia(nsMediaList* aMedia);
 
   void SetOwnerRule(css::ImportRule* aOwnerRule) { mOwnerRule = aOwnerRule; /* Not ref counted */ }
   css::ImportRule* GetOwnerRule() const { return mOwnerRule; }
+  // Workaround overloaded-virtual warning in GCC.
+  using StyleSheet::GetOwnerRule;
 
   nsXMLNameSpaceMap* GetNameSpaceMap() const { return mInner->mNameSpaceMap; }
 
   already_AddRefed<CSSStyleSheet> Clone(CSSStyleSheet* aCloneParent,
                                         css::ImportRule* aCloneOwnerRule,
                                         nsIDocument* aCloneDocument,
                                         nsINode* aCloneOwningNode) const;
 
@@ -195,47 +197,36 @@ public:
 
   bool UseForPresentation(nsPresContext* aPresContext,
                             nsMediaQueryResultCacheKey& aKey) const;
 
   nsresult ReparseSheet(const nsAString& aInput);
 
   void SetInRuleProcessorCache() { mInRuleProcessorCache = true; }
 
-  // nsIDOMStyleSheet interface
-  NS_IMETHOD GetParentStyleSheet(nsIDOMStyleSheet** aParentStyleSheet) final;
-  NS_IMETHOD GetMedia(nsIDOMMediaList** aMedia) final;
-
-  // nsIDOMCSSStyleSheet interface
-  NS_DECL_NSIDOMCSSSTYLESHEET
-
   // Function used as a callback to rebuild our inner's child sheet
   // list after we clone a unique inner for ourselves.
   static bool RebuildChildList(css::Rule* aRule, void* aBuilder);
 
   size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const;
 
   dom::Element* GetScopeElement() const { return mScopeElement; }
   void SetScopeElement(dom::Element* aScopeElement)
   {
     mScopeElement = aScopeElement;
   }
 
   // WebIDL StyleSheet API
-  using GetParentStyleSheet;
   nsMediaList* Media() final;
 
   // WebIDL CSSStyleSheet API
   // Can't be inline because we can't include ImportRule here.  And can't be
   // called GetOwnerRule because that would be ambiguous with the ImportRule
   // version.
   nsIDOMCSSRule* GetDOMOwnerRule() const final;
-  using StyleSheet::GetCssRules;
-  using StyleSheet::InsertRule;
-  using StyleSheet::DeleteRule;
 
   // WebIDL miscellaneous bits
   virtual JSObject* WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override;
 
   void WillDirty();
   void DidDirty();
 
 private:

--- a/layout/style/ServoStyleSheet.cpp
+++ b/layout/style/ServoStyleSheet.cpp
@@ -107,55 +107,26 @@ ServoStyleSheet::SizeOfIncludingThis(Mal
 #ifdef DEBUG
 void
 ServoStyleSheet::List(FILE* aOut, int32_t aIndex) const
 {
   MOZ_CRASH("stylo: not implemented");
 }
 #endif
 
-// nsIDOMStyleSheet implementation
-
-NS_IMETHODIMP
-ServoStyleSheet::GetParentStyleSheet(nsIDOMStyleSheet** aParentStyleSheet)
+nsMediaList*
+ServoStyleSheet::Media()
 {
-  return NS_ERROR_NOT_IMPLEMENTED;
-}
-
-NS_IMETHODIMP
-ServoStyleSheet::GetMedia(nsIDOMMediaList** aMedia)
-{
-  return NS_ERROR_NOT_IMPLEMENTED;
+  return nullptr;
 }
 
-// nsIDOMCSSStyleSheet implementation
-
-nsresult
-ServoStyleSheet::GetOwnerRule(nsIDOMCSSRule** aOwnerRule)
-{
-  return NS_ERROR_NOT_IMPLEMENTED;
-}
-
-nsresult
-ServoStyleSheet::GetCssRules(nsIDOMCSSRuleList** aCssRules)
+nsIDOMCSSRule*
+ServoStyleSheet::GetDOMOwnerRule() const
 {
-  return NS_ERROR_NOT_IMPLEMENTED;
-}
-
-nsresult
-ServoStyleSheet::InsertRule(const nsAString& rule,
-                            uint32_t aIndex, uint32_t* aReturn)
-{
-  return NS_ERROR_NOT_IMPLEMENTED;
-}
-
-nsresult
-ServoStyleSheet::DeleteRule(uint32_t aIndex)
-{
-  return NS_ERROR_NOT_IMPLEMENTED;
+  return nullptr;
 }
 
 CSSRuleList*
 ServoStyleSheet::GetCssRulesInternal(ErrorResult& aRv)
 {
   aRv.Throw(NS_ERROR_NOT_IMPLEMENTED);
   return nullptr;
 }

--- a/layout/style/ServoStyleSheet.h
+++ b/layout/style/ServoStyleSheet.h
@@ -46,22 +46,24 @@ public:
   size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const;
 
 #ifdef DEBUG
   void List(FILE* aOut = stdout, int32_t aIndex = 0) const;
 #endif
 
   RawServoStyleSheet* RawSheet() const { return mSheet; }
 
-  // nsIDOMStyleSheet interface
-  NS_IMETHOD GetParentStyleSheet(nsIDOMStyleSheet** aParentStyleSheet) final;
-  NS_IMETHOD GetMedia(nsIDOMMediaList** aMedia) final;
+  // WebIDL StyleSheet API
+  nsMediaList* Media() final;
 
-  // nsIDOMCSSStyleSheet interface
-  NS_DECL_NSIDOMCSSSTYLESHEET
+  // WebIDL CSSStyleSheet API
+  // Can't be inline because we can't include ImportRule here.  And can't be
+  // called GetOwnerRule because that would be ambiguous with the ImportRule
+  // version.
+  nsIDOMCSSRule* GetDOMOwnerRule() const final;
 
   void WillDirty() {}
   void DidDirty() {}
 
 protected:
   ~ServoStyleSheet();
 
   // Internal methods which do not have security check and completeness check.

--- a/layout/style/StyleSheet.cpp
+++ b/layout/style/StyleSheet.cpp
@@ -6,16 +6,18 @@
 
 #include "mozilla/StyleSheet.h"
 
 #include "mozilla/dom/ShadowRoot.h"
 #include "mozilla/ServoStyleSheet.h"
 #include "mozilla/StyleSheetInlines.h"
 #include "mozilla/CSSStyleSheet.h"
 
+#include "mozilla/dom/CSSRuleList.h"
+
 namespace mozilla {
 
 StyleSheet::StyleSheet(StyleBackendType aType, css::SheetParsingMode aParsingMode)
   : mDocument(nullptr)
   , mOwningNode(nullptr)
   , mParsingMode(aParsingMode)
   , mType(aType)
   , mDisabled(false)
@@ -130,16 +132,68 @@ StyleSheet::GetHref(nsAString& aHref)
 
 NS_IMETHODIMP
 StyleSheet::GetTitle(nsAString& aTitle)
 {
   aTitle.Assign(mTitle);
   return NS_OK;
 }
 
+// nsIDOMStyleSheet interface
+
+NS_IMETHODIMP
+StyleSheet::GetParentStyleSheet(nsIDOMStyleSheet** aParentStyleSheet)
+{
+  NS_ENSURE_ARG_POINTER(aParentStyleSheet);
+  NS_IF_ADDREF(*aParentStyleSheet = GetParentStyleSheet());
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+StyleSheet::GetMedia(nsIDOMMediaList** aMedia)
+{
+  NS_ADDREF(*aMedia = Media());
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+StyleSheet::GetOwnerRule(nsIDOMCSSRule** aOwnerRule)
+{
+  NS_IF_ADDREF(*aOwnerRule = GetDOMOwnerRule());
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+StyleSheet::GetCssRules(nsIDOMCSSRuleList** aCssRules)
+{
+  ErrorResult rv;
+  nsCOMPtr<nsIDOMCSSRuleList> rules =
+    GetCssRules(Some(nsContentUtils::SubjectPrincipal()), rv);
+  rules.forget(aCssRules);
+  return rv.StealNSResult();
+}
+
+NS_IMETHODIMP
+StyleSheet::InsertRule(const nsAString& aRule, uint32_t aIndex,
+                       uint32_t* aReturn)
+{
+  ErrorResult rv;
+  *aReturn =
+    InsertRule(aRule, aIndex, Some(nsContentUtils::SubjectPrincipal()), rv);
+  return rv.StealNSResult();
+}
+
+NS_IMETHODIMP
+StyleSheet::DeleteRule(uint32_t aIndex)
+{
+  ErrorResult rv;
+  DeleteRule(aIndex, Some(nsContentUtils::SubjectPrincipal()), rv);
+  return rv.StealNSResult();
+}
+
 // WebIDL CSSStyleSheet API
 
 #define FORWARD_INTERNAL(method_, args_) \
   if (IsServo()) { \
     return AsServo()->method_ args_; \
   } \
   return AsGecko()->method_ args_;
 

--- a/layout/style/StyleSheet.h
+++ b/layout/style/StyleSheet.h
@@ -157,18 +157,27 @@ public:
   // WebIDL miscellaneous bits
   inline dom::ParentObject GetParentObject() const;
 
   // nsIDOMStyleSheet interface
   NS_IMETHOD GetType(nsAString& aType) final;
   NS_IMETHOD GetDisabled(bool* aDisabled) final;
   NS_IMETHOD SetDisabled(bool aDisabled) final;
   NS_IMETHOD GetOwnerNode(nsIDOMNode** aOwnerNode) final;
+  NS_IMETHOD GetParentStyleSheet(nsIDOMStyleSheet** aParentStyleSheet) final;
   NS_IMETHOD GetHref(nsAString& aHref) final;
   NS_IMETHOD GetTitle(nsAString& aTitle) final;
+  NS_IMETHOD GetMedia(nsIDOMMediaList** aMedia) final;
+
+  // nsIDOMCSSStyleSheet
+  NS_IMETHOD GetOwnerRule(nsIDOMCSSRule** aOwnerRule) final;
+  NS_IMETHOD GetCssRules(nsIDOMCSSRuleList** aCssRules) final;
+  NS_IMETHOD InsertRule(const nsAString& aRule, uint32_t aIndex,
+                      uint32_t* aReturn) final;
+  NS_IMETHOD DeleteRule(uint32_t aIndex) final;
 
   // Changes to sheets should be inside of a WillDirty-DidDirty pair.
   // However, the calls do not need to be matched; it's ok to call
   // WillDirty and then make no change and skip the DidDirty call.
   inline void WillDirty();
   inline void DidDirty();
 
 private: