--- a/dom/bindings/Bindings.conf
+++ b/dom/bindings/Bindings.conf
@@ -231,21 +231,16 @@ DOMInterfaces = {
     'nativeType': 'nsCSSKeyframesRule',
     'headerFile': 'nsCSSRules.h',
 },
 
 'CSSLexer': {
     'wrapperCache': False
 },
 
-'CSSMediaRule': {
-    'nativeType': 'mozilla::css::MediaRule',
-    'headerFile': 'nsCSSRules.h',
-},
-
 'CSSMozDocumentRule': {
     'nativeType': 'mozilla::css::DocumentRule',
     'headerFile': 'nsCSSRules.h',
 },
 
 'CSSNamespaceRule': {
     'nativeType': 'mozilla::css::NameSpaceRule',
 },

new file mode 100644
--- /dev/null
+++ b/layout/style/CSSMediaRule.cpp
@@ -0,0 +1,72 @@
+/* -*- 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/. */
+
+#include "mozilla/dom/CSSMediaRule.h"
+
+#include "mozilla/dom/CSSMediaRuleBinding.h"
+#include "mozilla/dom/MediaList.h"
+
+namespace mozilla {
+namespace dom {
+
+NS_IMPL_ADDREF_INHERITED(CSSMediaRule, css::ConditionRule)
+NS_IMPL_RELEASE_INHERITED(CSSMediaRule, css::ConditionRule)
+
+// QueryInterface implementation for CSSMediaRule
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(CSSMediaRule)
+  NS_INTERFACE_MAP_ENTRY(nsIDOMCSSGroupingRule)
+  NS_INTERFACE_MAP_ENTRY(nsIDOMCSSConditionRule)
+  NS_INTERFACE_MAP_ENTRY(nsIDOMCSSMediaRule)
+NS_INTERFACE_MAP_END_INHERITING(css::ConditionRule)
+
+// nsIDOMCSSGroupingRule methods
+NS_IMETHODIMP
+CSSMediaRule::GetCssRules(nsIDOMCSSRuleList** aRuleList)
+{
+  return GroupRule::GetCssRules(aRuleList);
+}
+
+NS_IMETHODIMP
+CSSMediaRule::InsertRule(const nsAString& aRule,
+                         uint32_t aIndex, uint32_t* _retval)
+{
+  return GroupRule::InsertRule(aRule, aIndex, _retval);
+}
+
+NS_IMETHODIMP
+CSSMediaRule::DeleteRule(uint32_t aIndex)
+{
+  return GroupRule::DeleteRule(aIndex);
+}
+
+// nsIDOMCSSMediaRule methods
+NS_IMETHODIMP
+CSSMediaRule::GetMedia(nsIDOMMediaList* *aMedia)
+{
+  NS_ENSURE_ARG_POINTER(aMedia);
+  NS_IF_ADDREF(*aMedia = Media());
+  return NS_OK;
+}
+
+void
+CSSMediaRule::SetConditionText(const nsAString& aConditionText,
+                               ErrorResult& aRv)
+{
+  nsresult rv = static_cast<nsIDOMCSSConditionRule*>(this)->
+    SetConditionText(aConditionText);
+  if (NS_FAILED(rv)) {
+    aRv.Throw(rv);
+  }
+}
+
+/* virtual */ JSObject*
+CSSMediaRule::WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto)
+{
+  return CSSMediaRuleBinding::Wrap(aCx, this, aGivenProto);
+}
+
+} // namespace dom
+} // namespace mozilla

new file mode 100644
--- /dev/null
+++ b/layout/style/CSSMediaRule.h
@@ -0,0 +1,54 @@
+/* -*- 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_dom_CSSMediaRule_h
+#define mozilla_dom_CSSMediaRule_h
+
+#include "mozilla/css/GroupRule.h"
+#include "nsIDOMCSSMediaRule.h"
+
+namespace mozilla {
+namespace dom {
+
+class CSSMediaRule : public css::ConditionRule
+                   , public nsIDOMCSSMediaRule
+{
+protected:
+  using ConditionRule::ConditionRule;
+  virtual ~CSSMediaRule() {}
+
+public:
+  NS_DECL_ISUPPORTS_INHERITED
+
+  int32_t GetType() const override { return css::Rule::MEDIA_RULE; }
+
+  // XPCOM interface
+  using Rule::GetType;
+
+  // nsIDOMCSSGroupingRule interface
+  NS_DECL_NSIDOMCSSGROUPINGRULE
+
+  // nsIDOMCSSConditionRule interface
+  NS_IMETHOD SetConditionText(const nsAString& aConditionText) override = 0;
+
+  // nsIDOMCSSMediaRule interface
+  NS_DECL_NSIDOMCSSMEDIARULE
+
+  // WebIDL interface
+  uint16_t Type() const override { return nsIDOMCSSRule::MEDIA_RULE; }
+  // Our XPCOM GetConditionText is OK
+  void SetConditionText(const nsAString& aConditionText,
+                        ErrorResult& aRv) final;
+  virtual MediaList* Media() = 0;
+
+  JSObject* WrapObject(JSContext* aCx,
+                       JS::Handle<JSObject*> aGivenProto) override;
+};
+
+} // namespace dom
+} // namespace mozilla
+
+#endif // mozilla_dom_CSSMediaRule_h

--- a/layout/style/moz.build
+++ b/layout/style/moz.build
@@ -121,16 +121,17 @@ EXPORTS.mozilla += [
     'StyleSheet.h',
     'StyleSheetInfo.h',
     'StyleSheetInlines.h',
 ]
 
 EXPORTS.mozilla.dom += [
     'CSS.h',
     'CSSLexer.h',
+    'CSSMediaRule.h',
     'CSSRuleList.h',
     'CSSValue.h',
     'FontFace.h',
     'FontFaceSet.h',
     'FontFaceSetIterator.h',
     'MediaList.h',
     'MediaQueryList.h',
 ]
@@ -149,16 +150,17 @@ EXPORTS.mozilla.css += [
 ]
 
 UNIFIED_SOURCES += [
     'AnimationCollection.cpp',
     'BindingStyleRule.cpp',
     'CounterStyleManager.cpp',
     'CSS.cpp',
     'CSSLexer.cpp',
+    'CSSMediaRule.cpp',
     'CSSRuleList.cpp',
     'CSSStyleSheet.cpp',
     'CSSVariableDeclarations.cpp',
     'CSSVariableResolver.cpp',
     'CSSVariableValues.cpp',
     'Declaration.cpp',
     'DocumentStyleRootIterator.cpp',
     'ErrorReporter.cpp',

--- a/layout/style/nsCSSRules.cpp
+++ b/layout/style/nsCSSRules.cpp
@@ -31,17 +31,16 @@
 #include "nsError.h"
 #include "nsStyleUtil.h"
 #include "mozilla/DeclarationBlockInlines.h"
 #include "nsCSSParser.h"
 #include "nsDOMClassInfoID.h"
 #include "mozilla/dom/CSSStyleDeclarationBinding.h"
 #include "mozilla/dom/CSSNamespaceRuleBinding.h"
 #include "mozilla/dom/CSSImportRuleBinding.h"
-#include "mozilla/dom/CSSMediaRuleBinding.h"
 #include "mozilla/dom/CSSSupportsRuleBinding.h"
 #include "mozilla/dom/CSSMozDocumentRuleBinding.h"
 #include "mozilla/dom/CSSPageRuleBinding.h"
 #include "mozilla/dom/CSSFontFaceRuleBinding.h"
 #include "mozilla/dom/CSSFontFeatureValuesRuleBinding.h"
 #include "mozilla/dom/CSSKeyframeRuleBinding.h"
 #include "mozilla/dom/CSSKeyframesRuleBinding.h"
 #include "mozilla/dom/CSSCounterStyleRuleBinding.h"
@@ -359,48 +358,45 @@ ImportRule::WrapObject(JSContext* aCx,
 {
   return CSSImportRuleBinding::Wrap(aCx, this, aGivenProto);
 }
 
 // -------------------------------------------
 // nsICSSMediaRule
 //
 MediaRule::MediaRule(uint32_t aLineNumber, uint32_t aColumnNumber)
-  : ConditionRule(aLineNumber, aColumnNumber)
+  : CSSMediaRule(aLineNumber, aColumnNumber)
 {
 }
 
 MediaRule::MediaRule(const MediaRule& aCopy)
-  : ConditionRule(aCopy)
+  : CSSMediaRule(aCopy)
 {
   if (aCopy.mMedia) {
     mMedia = aCopy.mMedia->Clone().downcast<nsMediaList>();
     // XXXldb This doesn't really make sense.
     mMedia->SetStyleSheet(aCopy.GetStyleSheet());
   }
 }
 
 MediaRule::~MediaRule()
 {
   if (mMedia) {
     mMedia->SetStyleSheet(nullptr);
   }
 }
 
-NS_IMPL_ADDREF_INHERITED(MediaRule, ConditionRule)
-NS_IMPL_RELEASE_INHERITED(MediaRule, ConditionRule)
+NS_IMPL_ADDREF_INHERITED(MediaRule, CSSMediaRule)
+NS_IMPL_RELEASE_INHERITED(MediaRule, CSSMediaRule)
 
 // QueryInterface implementation for MediaRule
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(MediaRule)
-  NS_INTERFACE_MAP_ENTRY(nsIDOMCSSGroupingRule)
-  NS_INTERFACE_MAP_ENTRY(nsIDOMCSSConditionRule)
-  NS_INTERFACE_MAP_ENTRY(nsIDOMCSSMediaRule)
-NS_INTERFACE_MAP_END_INHERITING(ConditionRule)
-
-NS_IMPL_CYCLE_COLLECTION_INHERITED(MediaRule, ConditionRule,
+NS_INTERFACE_MAP_END_INHERITING(CSSMediaRule)
+
+NS_IMPL_CYCLE_COLLECTION_INHERITED(MediaRule, CSSMediaRule,
                                    mMedia)
 
 /* virtual */ void
 MediaRule::SetStyleSheet(StyleSheet* aSheet)
 {
   if (mMedia) {
     // Set to null so it knows it's leaving one sheet and joining another.
     mMedia->SetStyleSheet(nullptr);
@@ -434,125 +430,71 @@ MediaRule::List(FILE* out, int32_t aInde
   fprintf_stderr(out, "%s", str.get());
 
   GroupRule::List(out, aIndent);
 
   fprintf_stderr(out, "%s}\n", indentStr.get());
 }
 #endif
 
-/* virtual */ int32_t
-MediaRule::GetType() const
-{
-  return Rule::MEDIA_RULE;
-}
-
 /* virtual */ already_AddRefed<Rule>
 MediaRule::Clone() const
 {
   RefPtr<Rule> clone = new MediaRule(*this);
   return clone.forget();
 }
 
 nsresult
 MediaRule::SetMedia(nsMediaList* aMedia)
 {
   mMedia = aMedia;
   if (aMedia)
     mMedia->SetStyleSheet(GetStyleSheet());
   return NS_OK;
 }
 
-uint16_t
-MediaRule::Type() const
-{
-  return nsIDOMCSSRule::MEDIA_RULE;
-}
-
 MediaList*
-MediaRule::Media() const
+MediaRule::Media()
 {
   // In practice, if we end up being parsed at all, we have non-null mMedia.  So
   // it's OK to claim we don't return null here.
   return mMedia;
 }
 
 void
 MediaRule::GetCssTextImpl(nsAString& aCssText) const
 {
   aCssText.AssignLiteral("@media ");
   AppendConditionText(aCssText);
   GroupRule::AppendRulesToCssText(aCssText);
 }
 
-// nsIDOMCSSGroupingRule methods
-NS_IMETHODIMP
-MediaRule::GetCssRules(nsIDOMCSSRuleList* *aRuleList)
-{
-  return GroupRule::GetCssRules(aRuleList);
-}
-
-NS_IMETHODIMP
-MediaRule::InsertRule(const nsAString & aRule, uint32_t aIndex, uint32_t* _retval)
-{
-  return GroupRule::InsertRule(aRule, aIndex, _retval);
-}
-
-NS_IMETHODIMP
-MediaRule::DeleteRule(uint32_t aIndex)
-{
-  return GroupRule::DeleteRule(aIndex);
-}
-
 // nsIDOMCSSConditionRule methods
 NS_IMETHODIMP
 MediaRule::GetConditionText(nsAString& aConditionText)
 {
   aConditionText.Truncate(0);
   AppendConditionText(aConditionText);
   return NS_OK;
 }
 
 NS_IMETHODIMP
 MediaRule::SetConditionText(const nsAString& aConditionText)
 {
-  ErrorResult rv;
-  SetConditionText(aConditionText, rv);
-  return rv.StealNSResult();
-}
-
-void
-MediaRule::SetConditionText(const nsAString& aConditionText,
-                            ErrorResult& aRv)
-{
   if (!mMedia) {
     RefPtr<nsMediaList> media = new nsMediaList();
     media->SetStyleSheet(GetStyleSheet());
     nsresult rv = media->SetMediaText(aConditionText);
     if (NS_SUCCEEDED(rv)) {
       mMedia = media;
-    } else {
-      aRv.Throw(rv);
     }
-    return;
-  }
-
-  nsresult rv = mMedia->SetMediaText(aConditionText);
-  if (NS_FAILED(rv)) {
-    aRv.Throw(rv);
+    return rv;
   }
-}
-
-// nsIDOMCSSMediaRule methods
-NS_IMETHODIMP
-MediaRule::GetMedia(nsIDOMMediaList* *aMedia)
-{
-  NS_ENSURE_ARG_POINTER(aMedia);
-  NS_IF_ADDREF(*aMedia = mMedia);
-  return NS_OK;
+
+  return mMedia->SetMediaText(aConditionText);
 }
 
 // GroupRule interface
 /* virtual */ bool
 MediaRule::UseForPresentation(nsPresContext* aPresContext,
                                    nsMediaQueryResultCacheKey& aKey)
 {
   if (mMedia) {
@@ -569,23 +511,16 @@ MediaRule::SizeOfIncludingThis(MallocSiz
 
   // Measurement of the following members may be added later if DMD finds it is
   // worthwhile:
   // - mMedia
 
   return n;
 }
 
-/* virtual */ JSObject*
-MediaRule::WrapObject(JSContext* aCx,
-                      JS::Handle<JSObject*> aGivenProto)
-{
-  return CSSMediaRuleBinding::Wrap(aCx, this, aGivenProto);
-}
-
 void
 MediaRule::AppendConditionText(nsAString& aOutput) const
 {
   if (mMedia) {
     nsAutoString mediaText;
     mMedia->GetText(mediaText);
     aOutput.Append(mediaText);
   }

--- a/layout/style/nsCSSRules.h
+++ b/layout/style/nsCSSRules.h
@@ -12,27 +12,27 @@
 #include "Declaration.h"
 #include "StyleRule.h"
 #include "gfxFontFeatures.h"
 #include "mozilla/Attributes.h"
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/Move.h"
 #include "mozilla/SheetType.h"
 #include "mozilla/css/GroupRule.h"
+#include "mozilla/dom/CSSMediaRule.h"
 #include "mozilla/dom/FontFace.h"
 #include "nsAutoPtr.h"
 #include "nsCSSPropertyID.h"
 #include "nsCSSValue.h"
 #include "nsDOMCSSDeclaration.h"
 #include "nsIDOMCSSConditionRule.h"
 #include "nsIDOMCSSCounterStyleRule.h"
 #include "nsIDOMCSSFontFaceRule.h"
 #include "nsIDOMCSSFontFeatureValuesRule.h"
 #include "nsIDOMCSSGroupingRule.h"
-#include "nsIDOMCSSMediaRule.h"
 #include "nsIDOMCSSMozDocumentRule.h"
 #include "nsIDOMCSSPageRule.h"
 #include "nsIDOMCSSSupportsRule.h"
 #include "nsIDOMCSSKeyframeRule.h"
 #include "nsIDOMCSSKeyframesRule.h"
 #include "nsTArray.h"
 
 class nsMediaList;
@@ -42,73 +42,57 @@ namespace mozilla {
 class ErrorResult;
 
 namespace dom {
 class MediaList;
 }
 
 namespace css {
 
-class MediaRule final : public ConditionRule,
-                        public nsIDOMCSSMediaRule
+class MediaRule final : public dom::CSSMediaRule
 {
 public:
   MediaRule(uint32_t aLineNumber, uint32_t aColumnNumber);
 private:
   MediaRule(const MediaRule& aCopy);
   ~MediaRule();
 public:
-
-  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(MediaRule, ConditionRule)
   NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(MediaRule, dom::CSSMediaRule)
 
   // Rule methods
 #ifdef DEBUG
   virtual void List(FILE* out = stdout, int32_t aIndent = 0) const override;
 #endif
   virtual void SetStyleSheet(mozilla::StyleSheet* aSheet) override; //override GroupRule
   mozilla::CSSStyleSheet* GetStyleSheet() const
   {
     mozilla::StyleSheet* sheet = GroupRule::GetStyleSheet();
     return sheet ? sheet->AsGecko() : nullptr;
   }
-  virtual int32_t GetType() const override;
-  using Rule::GetType;
   virtual already_AddRefed<Rule> Clone() const override;
 
-  // nsIDOMCSSGroupingRule interface
-  NS_DECL_NSIDOMCSSGROUPINGRULE
-
   // nsIDOMCSSConditionRule interface
   NS_DECL_NSIDOMCSSCONDITIONRULE
 
-  // nsIDOMCSSMediaRule interface
-  NS_DECL_NSIDOMCSSMEDIARULE
-
   // rest of GroupRule
   virtual bool UseForPresentation(nsPresContext* aPresContext,
                                     nsMediaQueryResultCacheKey& aKey) override;
 
   // @media rule methods
   nsresult SetMedia(nsMediaList* aMedia);
 
   // WebIDL interface
-  uint16_t Type() const override;
   void GetCssTextImpl(nsAString& aCssText) const override;
-  // Our XPCOM GetConditionText is OK
-  virtual void SetConditionText(const nsAString& aConditionText,
-                                ErrorResult& aRv) override;
-  dom::MediaList* Media() const;
+  using CSSMediaRule::SetConditionText;
+  dom::MediaList* Media() override;
   
   virtual size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf)
     const override MOZ_MUST_OVERRIDE;
 
-  virtual JSObject* WrapObject(JSContext* aCx,
-                               JS::Handle<JSObject*> aGivenProto) override;
-
 protected:
   void AppendConditionText(nsAString& aOutput) const;
 
   RefPtr<nsMediaList> mMedia;
 };
 
 class DocumentRule final : public ConditionRule,
                            public nsIDOMCSSMozDocumentRule