--- a/dom/bindings/Bindings.conf
+++ b/dom/bindings/Bindings.conf
@@ -253,21 +253,16 @@ DOMInterfaces = {
     'nativeType': 'mozilla::BindingStyleRule',
 },
 
 'CSSStyleSheet': {
     'nativeType': 'mozilla::StyleSheet',
     'binaryNames': { 'ownerRule': 'DOMOwnerRule' },
 },
 
-'CSSSupportsRule': {
-    'nativeType': 'mozilla::CSSSupportsRule',
-    'headerFile': 'nsCSSRules.h',
-},
-
 'CSSValue': {
     'concrete': False
 },
 
 'CSSValueList': {
     'nativeType': 'nsDOMCSSValueList'
 },
 

new file mode 100644
--- /dev/null
+++ b/layout/style/CSSSupportsRule.cpp
@@ -0,0 +1,60 @@
+/* -*- 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/CSSSupportsRule.h"
+
+#include "mozilla/dom/CSSSupportsRuleBinding.h"
+
+using namespace mozilla::css;
+
+namespace mozilla {
+namespace dom {
+
+NS_IMPL_ADDREF_INHERITED(CSSSupportsRule, css::ConditionRule)
+NS_IMPL_RELEASE_INHERITED(CSSSupportsRule, css::ConditionRule)
+
+// QueryInterface implementation for CSSSupportsRule
+NS_INTERFACE_MAP_BEGIN(CSSSupportsRule)
+  NS_INTERFACE_MAP_ENTRY(nsIDOMCSSGroupingRule)
+  NS_INTERFACE_MAP_ENTRY(nsIDOMCSSConditionRule)
+  NS_INTERFACE_MAP_ENTRY(nsIDOMCSSSupportsRule)
+NS_INTERFACE_MAP_END_INHERITING(ConditionRule)
+
+// nsIDOMCSSGroupingRule methods
+NS_IMETHODIMP
+CSSSupportsRule::GetCssRules(nsIDOMCSSRuleList** aRuleList)
+{
+  return GroupRule::GetCssRules(aRuleList);
+}
+
+NS_IMETHODIMP
+CSSSupportsRule::InsertRule(const nsAString & aRule, uint32_t aIndex, uint32_t* _retval)
+{
+  return GroupRule::InsertRule(aRule, aIndex, _retval);
+}
+
+NS_IMETHODIMP
+CSSSupportsRule::DeleteRule(uint32_t aIndex)
+{
+  return GroupRule::DeleteRule(aIndex);
+}
+
+void
+CSSSupportsRule::SetConditionText(const nsAString& aConditionText,
+                                  ErrorResult& aRv)
+{
+  aRv = SetConditionText(aConditionText);
+}
+
+/* virtual */ JSObject*
+CSSSupportsRule::WrapObject(JSContext* aCx,
+                            JS::Handle<JSObject*> aGivenProto)
+{
+  return CSSSupportsRuleBinding::Wrap(aCx, this, aGivenProto);
+}
+
+} // namespace dom
+} // namespace mozilla

new file mode 100644
--- /dev/null
+++ b/layout/style/CSSSupportsRule.h
@@ -0,0 +1,51 @@
+/* -*- 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_CSSSupportsRule_h
+#define mozilla_dom_CSSSupportsRule_h
+
+#include "mozilla/css/GroupRule.h"
+#include "nsIDOMCSSSupportsRule.h"
+
+namespace mozilla {
+namespace dom {
+
+class CSSSupportsRule : public css::ConditionRule
+                      , public nsIDOMCSSSupportsRule
+{
+protected:
+  using ConditionRule::ConditionRule;
+  virtual ~CSSSupportsRule() {}
+
+public:
+  NS_DECL_ISUPPORTS_INHERITED
+
+  int32_t GetType() const override { return css::Rule::SUPPORTS_RULE; }
+  using Rule::GetType;
+
+  // nsIDOMCSSGroupingRule interface
+  NS_DECL_NSIDOMCSSGROUPINGRULE
+
+  // nsIDOMCSSConditionRule interface
+  NS_IMETHOD SetConditionText(const nsAString& aConditionText) override = 0;
+
+  // nsIDOMCSSSupportsRule interface
+  NS_DECL_NSIDOMCSSSUPPORTSRULE
+
+  // WebIDL interface
+  uint16_t Type() const override { return nsIDOMCSSRule::SUPPORTS_RULE; }
+  // Our XPCOM GetConditionText is OK
+  void SetConditionText(const nsAString& aConditionText,
+                        ErrorResult& aRv) final;
+
+  JSObject* WrapObject(JSContext* aCx,
+                       JS::Handle<JSObject*> aGivenProto) override;
+};
+
+} // namespace dom
+} // namespace mozilla
+
+#endif // mozilla_dom_CSSSupportsRule_h

--- a/layout/style/moz.build
+++ b/layout/style/moz.build
@@ -129,16 +129,17 @@ EXPORTS.mozilla += [
 
 EXPORTS.mozilla.dom += [
     'CSS.h',
     'CSSLexer.h',
     'CSSMediaRule.h',
     'CSSNamespaceRule.h',
     'CSSPageRule.h',
     'CSSRuleList.h',
+    'CSSSupportsRule.h',
     'CSSValue.h',
     'FontFace.h',
     'FontFaceSet.h',
     'FontFaceSetIterator.h',
     'MediaList.h',
     'MediaQueryList.h',
 ]
 
@@ -160,16 +161,17 @@ UNIFIED_SOURCES += [
     'BindingStyleRule.cpp',
     'CounterStyleManager.cpp',
     'CSS.cpp',
     'CSSLexer.cpp',
     'CSSMediaRule.cpp',
     'CSSPageRule.cpp',
     'CSSRuleList.cpp',
     'CSSStyleSheet.cpp',
+    'CSSSupportsRule.cpp',
     'CSSVariableDeclarations.cpp',
     'CSSVariableResolver.cpp',
     'CSSVariableValues.cpp',
     'Declaration.cpp',
     'DocumentStyleRootIterator.cpp',
     'ErrorReporter.cpp',
     'FontFace.cpp',
     'FontFaceSet.cpp',

--- a/layout/style/nsCSSRules.cpp
+++ b/layout/style/nsCSSRules.cpp
@@ -31,17 +31,16 @@
 #include "nsContentUtils.h"
 #include "nsError.h"
 #include "nsStyleUtil.h"
 #include "mozilla/DeclarationBlockInlines.h"
 #include "nsCSSParser.h"
 #include "nsDOMClassInfoID.h"
 #include "mozilla/dom/CSSStyleDeclarationBinding.h"
 #include "mozilla/dom/CSSImportRuleBinding.h"
-#include "mozilla/dom/CSSSupportsRuleBinding.h"
 #include "mozilla/dom/CSSMozDocumentRuleBinding.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"
 #include "StyleRule.h"
 #include "nsFont.h"
@@ -2267,28 +2266,28 @@ nsCSSPageRule::SizeOfIncludingThis(Mallo
   return aMallocSizeOf(this);
 }
 
 namespace mozilla {
 
 CSSSupportsRule::CSSSupportsRule(bool aConditionMet,
                                  const nsString& aCondition,
                                  uint32_t aLineNumber, uint32_t aColumnNumber)
-  : css::ConditionRule(aLineNumber, aColumnNumber)
+  : dom::CSSSupportsRule(aLineNumber, aColumnNumber)
   , mUseGroup(aConditionMet)
   , mCondition(aCondition)
 {
 }
 
 CSSSupportsRule::~CSSSupportsRule()
 {
 }
 
 CSSSupportsRule::CSSSupportsRule(const CSSSupportsRule& aCopy)
-  : css::ConditionRule(aCopy),
+  : dom::CSSSupportsRule(aCopy),
     mUseGroup(aCopy.mUseGroup),
     mCondition(aCopy.mCondition)
 {
 }
 
 #ifdef DEBUG
 /* virtual */ void
 CSSSupportsRule::List(FILE* out, int32_t aIndent) const
@@ -2302,22 +2301,16 @@ CSSSupportsRule::List(FILE* out, int32_t
                  indentStr.get(), NS_ConvertUTF16toUTF8(mCondition).get());
 
   css::GroupRule::List(out, aIndent);
 
   fprintf_stderr(out, "%s}\n", indentStr.get());
 }
 #endif
 
-/* virtual */ int32_t
-CSSSupportsRule::GetType() const
-{
-  return Rule::SUPPORTS_RULE;
-}
-
 /* virtual */ already_AddRefed<mozilla::css::Rule>
 CSSSupportsRule::Clone() const
 {
   RefPtr<css::Rule> clone = new CSSSupportsRule(*this);
   return clone.forget();
 }
 
 /* virtual */ bool
@@ -2327,91 +2320,49 @@ CSSSupportsRule::UseForPresentation(nsPr
   return mUseGroup;
 }
 
 NS_IMPL_ADDREF_INHERITED(CSSSupportsRule, css::ConditionRule)
 NS_IMPL_RELEASE_INHERITED(CSSSupportsRule, css::ConditionRule)
 
 // QueryInterface implementation for CSSSupportsRule
 NS_INTERFACE_MAP_BEGIN(CSSSupportsRule)
-  NS_INTERFACE_MAP_ENTRY(nsIDOMCSSGroupingRule)
-  NS_INTERFACE_MAP_ENTRY(nsIDOMCSSConditionRule)
-  NS_INTERFACE_MAP_ENTRY(nsIDOMCSSSupportsRule)
-NS_INTERFACE_MAP_END_INHERITING(ConditionRule)
-
-uint16_t
-CSSSupportsRule::Type() const
-{
-  return nsIDOMCSSRule::SUPPORTS_RULE;
-}
+NS_INTERFACE_MAP_END_INHERITING(dom::CSSSupportsRule)
 
 void
 CSSSupportsRule::GetCssTextImpl(nsAString& aCssText) const
 {
   aCssText.AssignLiteral("@supports ");
   aCssText.Append(mCondition);
   css::GroupRule::AppendRulesToCssText(aCssText);
 }
 
-// nsIDOMCSSGroupingRule methods
-NS_IMETHODIMP
-CSSSupportsRule::GetCssRules(nsIDOMCSSRuleList* *aRuleList)
-{
-  return css::GroupRule::GetCssRules(aRuleList);
-}
-
-NS_IMETHODIMP
-CSSSupportsRule::InsertRule(const nsAString & aRule, uint32_t aIndex, uint32_t* _retval)
-{
-  return css::GroupRule::InsertRule(aRule, aIndex, _retval);
-}
-
-NS_IMETHODIMP
-CSSSupportsRule::DeleteRule(uint32_t aIndex)
-{
-  return css::GroupRule::DeleteRule(aIndex);
-}
-
 // nsIDOMCSSConditionRule methods
 NS_IMETHODIMP
 CSSSupportsRule::GetConditionText(nsAString& aConditionText)
 {
   aConditionText.Assign(mCondition);
   return NS_OK;
 }
 
 NS_IMETHODIMP
 CSSSupportsRule::SetConditionText(const nsAString& aConditionText)
 {
   return NS_ERROR_NOT_IMPLEMENTED;
 }
 
-void
-CSSSupportsRule::SetConditionText(const nsAString& aConditionText,
-                                  ErrorResult& aRv)
-{
-  aRv.Throw(NS_ERROR_NOT_IMPLEMENTED);
-}
-
 /* virtual */ size_t
 CSSSupportsRule::SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const
 {
   size_t n = aMallocSizeOf(this);
   n += css::GroupRule::SizeOfExcludingThis(aMallocSizeOf);
   n += mCondition.SizeOfExcludingThisIfUnshared(aMallocSizeOf);
   return n;
 }
 
-/* virtual */ JSObject*
-CSSSupportsRule::WrapObject(JSContext* aCx,
-                            JS::Handle<JSObject*> aGivenProto)
-{
-  return CSSSupportsRuleBinding::Wrap(aCx, this, aGivenProto);
-}
-
 } // namespace mozilla
 
 // -------------------------------------------
 // nsCSSCounterStyleRule
 //
 
 nsCSSCounterStyleRule::nsCSSCounterStyleRule(const nsCSSCounterStyleRule& aCopy)
   : Rule(aCopy)

--- a/layout/style/nsCSSRules.h
+++ b/layout/style/nsCSSRules.h
@@ -14,16 +14,17 @@
 #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/CSSPageRule.h"
+#include "mozilla/dom/CSSSupportsRule.h"
 #include "nsAutoPtr.h"
 #include "nsCSSPropertyID.h"
 #include "nsCSSValue.h"
 #include "nsDOMCSSDeclaration.h"
 #include "nsIDOMCSSConditionRule.h"
 #include "nsIDOMCSSCounterStyleRule.h"
 #include "nsIDOMCSSFontFeatureValuesRule.h"
 #include "nsIDOMCSSGroupingRule.h"
@@ -441,57 +442,42 @@ public:
 private:
   RefPtr<mozilla::css::Declaration>     mDeclaration;
   // lazily created when needed:
   RefPtr<nsCSSPageStyleDeclaration>     mDOMDeclaration;
 };
 
 namespace mozilla {
 
-class CSSSupportsRule final : public css::ConditionRule,
-                              public nsIDOMCSSSupportsRule
+class CSSSupportsRule final : public dom::CSSSupportsRule
 {
 public:
   CSSSupportsRule(bool aConditionMet, const nsString& aCondition,
                   uint32_t aLineNumber, uint32_t aColumnNumber);
   CSSSupportsRule(const CSSSupportsRule& aCopy);
 
   // Rule methods
 #ifdef DEBUG
   virtual void List(FILE* out = stdout, int32_t aIndent = 0) const override;
 #endif
-  virtual int32_t GetType() const override;
-  using Rule::GetType;
   virtual already_AddRefed<mozilla::css::Rule> Clone() const override;
   virtual bool UseForPresentation(nsPresContext* aPresContext,
                                   nsMediaQueryResultCacheKey& aKey) override;
 
   NS_DECL_ISUPPORTS_INHERITED
 
-  // nsIDOMCSSGroupingRule interface
-  NS_DECL_NSIDOMCSSGROUPINGRULE
-
   // nsIDOMCSSConditionRule interface
   NS_DECL_NSIDOMCSSCONDITIONRULE
 
-  // nsIDOMCSSSupportsRule interface
-  NS_DECL_NSIDOMCSSSUPPORTSRULE
-
   // 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;
+  using dom::CSSSupportsRule::SetConditionText;
 
   virtual size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const override;
 
-  virtual JSObject* WrapObject(JSContext* aCx,
-                               JS::Handle<JSObject*> aGivenProto) override;
-
 protected:
   virtual ~CSSSupportsRule();
 
   bool mUseGroup;
   nsString mCondition;
 };
 
 } // namespace mozilla