--- a/dom/base/nsDOMClassInfo.cpp
+++ b/dom/base/nsDOMClassInfo.cpp
@@ -71,17 +71,16 @@
 // CSS related includes
 #include "nsCSSRules.h"
 #include "nsIDOMCSSRule.h"
 #include "nsMemory.h"
 
 // includes needed for the prototype chain interfaces
 #include "nsIDOMCSSKeyframeRule.h"
 #include "nsIDOMCSSKeyframesRule.h"
-#include "nsIDOMCSSFontFaceRule.h"
 #include "nsIDOMCSSCounterStyleRule.h"
 #include "nsIDOMXULCommandDispatcher.h"
 #include "nsIControllers.h"
 #ifdef MOZ_XUL
 #include "nsITreeSelection.h"
 #include "nsITreeContentView.h"
 #include "nsITreeView.h"
 #include "nsIXULTemplateBuilder.h"
@@ -200,20 +199,16 @@ static nsDOMClassInfoData sClassInfoData
 #ifdef MOZ_XUL
   NS_DEFINE_CHROME_XBL_CLASSINFO_DATA(XULTemplateBuilder, nsDOMGenericSH,
                                       DEFAULT_SCRIPTABLE_FLAGS)
 
   NS_DEFINE_CHROME_XBL_CLASSINFO_DATA(XULTreeBuilder, nsDOMGenericSH,
                                       DEFAULT_SCRIPTABLE_FLAGS)
 #endif
 
-  NS_DEFINE_CLASSINFO_DATA(CSSFontFaceRule, nsCSSRuleSH,
-                           DOM_DEFAULT_SCRIPTABLE_FLAGS |
-                           nsIXPCScriptable::WANT_PRECREATE)
-
   NS_DEFINE_CHROME_ONLY_CLASSINFO_DATA(ContentFrameMessageManager,
                                        nsMessageManagerSH<nsEventTargetSH>,
                                        DOM_DEFAULT_SCRIPTABLE_FLAGS |
                                        nsIXPCScriptable::WANT_ENUMERATE |
                                        nsIXPCScriptable::IS_GLOBAL_OBJECT)
   NS_DEFINE_CHROME_ONLY_CLASSINFO_DATA(ContentProcessMessageManager,
                                        nsMessageManagerSH<nsDOMGenericSH>,
                                        DOM_DEFAULT_SCRIPTABLE_FLAGS |
@@ -520,21 +515,16 @@ nsDOMClassInfo::Init()
 
   DOM_CLASSINFO_MAP_BEGIN(XULTreeBuilder, nsIXULTreeBuilder)
     DOM_CLASSINFO_MAP_ENTRY(nsIXULTreeBuilder)
     DOM_CLASSINFO_MAP_ENTRY(nsIXULTemplateBuilder)
     DOM_CLASSINFO_MAP_ENTRY(nsITreeView)
   DOM_CLASSINFO_MAP_END
 #endif
 
-  DOM_CLASSINFO_MAP_BEGIN(CSSFontFaceRule, nsIDOMCSSFontFaceRule)
-    DOM_CLASSINFO_MAP_ENTRY(nsIDOMCSSRule)
-    DOM_CLASSINFO_MAP_ENTRY(nsIDOMCSSFontFaceRule)
-  DOM_CLASSINFO_MAP_END
-
   DOM_CLASSINFO_MAP_BEGIN_NO_CLASS_IF(ContentFrameMessageManager, nsISupports)
     DOM_CLASSINFO_MAP_ENTRY(nsIDOMEventTarget)
     DOM_CLASSINFO_MAP_ENTRY(nsIMessageListenerManager)
     DOM_CLASSINFO_MAP_ENTRY(nsIMessageSender)
     DOM_CLASSINFO_MAP_ENTRY(nsISyncMessageSender)
     DOM_CLASSINFO_MAP_ENTRY(nsIContentFrameMessageManager)
   DOM_CLASSINFO_MAP_END
 

--- a/dom/base/nsDOMClassInfoID.h
+++ b/dom/base/nsDOMClassInfoID.h
@@ -29,19 +29,16 @@ enum nsDOMClassInfoID
   eDOMClassInfo_TreeContentView_id,
 #endif
 
 #ifdef MOZ_XUL
   eDOMClassInfo_XULTemplateBuilder_id,
   eDOMClassInfo_XULTreeBuilder_id,
 #endif
 
-  // @font-face in CSS
-  eDOMClassInfo_CSSFontFaceRule_id,
-
   eDOMClassInfo_ContentFrameMessageManager_id,
   eDOMClassInfo_ContentProcessMessageManager_id,
   eDOMClassInfo_ChromeMessageBroadcaster_id,
   eDOMClassInfo_ChromeMessageSender_id,
 
   eDOMClassInfo_CSSKeyframeRule_id,
   eDOMClassInfo_CSSKeyframesRule_id,
 

--- a/dom/base/nsWrapperCache.h
+++ b/dom/base/nsWrapperCache.h
@@ -18,17 +18,16 @@ namespace mozilla {
 namespace dom {
 class TabChildGlobal;
 class ProcessGlobal;
 } // namespace dom
 } // namespace mozilla
 class SandboxPrivate;
 class nsInProcessTabChildGlobal;
 class nsWindowRoot;
-class nsCSSFontFaceRule;
 class nsCSSFontFeatureValuesRule;
 class nsCSSKeyframeRule;
 class nsCSSKeyframesRule;
 class nsCSSCounterStyleRule;
 
 #define NS_WRAPPERCACHE_IID \
 { 0x6f3179a1, 0x36f7, 0x4a5c, \
   { 0x8c, 0xf1, 0xad, 0xc8, 0x7c, 0xde, 0x3e, 0x87 } }
@@ -280,17 +279,16 @@ private:
   // Friend declarations for things that need to be able to call
   // SetIsNotDOMBinding().  The goal is to get rid of all of these, and
   // SetIsNotDOMBinding() too.
   friend class mozilla::dom::TabChildGlobal;
   friend class mozilla::dom::ProcessGlobal;
   friend class SandboxPrivate;
   friend class nsInProcessTabChildGlobal;
   friend class nsWindowRoot;
-  friend class nsCSSFontFaceRule;
   friend class nsCSSFontFeatureValuesRule;
   friend class nsCSSKeyframeRule;
   friend class nsCSSKeyframesRule;
   friend class nsCSSCounterStyleRule;
   void SetIsNotDOMBinding()
   {
     MOZ_ASSERT(!mWrapper && !(GetWrapperFlags() & ~WRAPPER_IS_NOT_DOM_BINDING),
                "This flag should be set before creating any wrappers.");

--- a/dom/bindings/Bindings.conf
+++ b/dom/bindings/Bindings.conf
@@ -197,16 +197,21 @@ DOMInterfaces = {
 },
 
 'CSSConditionRule': {
     'concrete': False,
     'nativeType': 'mozilla::css::ConditionRule',
     'headerFile': 'mozilla/css/GroupRule.h',
 },
 
+'CSSFontFaceRule': {
+    'nativeType': 'nsCSSFontFaceRule',
+    'headerFile': 'nsCSSRules.h',
+},
+
 'CSSGroupingRule': {
     'concrete': False,
     'nativeType': 'mozilla::css::GroupRule',
 },
 
 'CSSImportRule': {
     'nativeType': 'mozilla::css::ImportRule',
 },

new file mode 100644
--- /dev/null
+++ b/dom/webidl/CSSFontFaceRule.webidl
@@ -0,0 +1,15 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/.
+ *
+ * The origin of this IDL file is
+ * https://drafts.csswg.org/css-fonts/#om-fontface
+ */
+
+// https://drafts.csswg.org/css-fonts/#om-fontface
+// But we implement a very old draft, apparently....
+// See bug 1058408 for implementing the current spec.
+interface CSSFontFaceRule : CSSRule {
+  [SameObject] readonly attribute CSSStyleDeclaration style;
+};

--- a/dom/webidl/moz.build
+++ b/dom/webidl/moz.build
@@ -85,16 +85,17 @@ WEBIDL_FILES = [
     'Coordinates.webidl',
     'CreateOfferRequest.webidl',
     'Crypto.webidl',
     'CSPDictionaries.webidl',
     'CSPReport.webidl',
     'CSS.webidl',
     'CSSAnimation.webidl',
     'CSSConditionRule.webidl',
+    'CSSFontFaceRule.webidl',
     'CSSGroupingRule.webidl',
     'CSSImportRule.webidl',
     'CSSLexer.webidl',
     'CSSMediaRule.webidl',
     'CSSMozDocumentRule.webidl',
     'CSSNamespaceRule.webidl',
     'CSSPageRule.webidl',
     'CSSPrimitiveValue.webidl',

--- a/layout/style/nsCSSRules.cpp
+++ b/layout/style/nsCSSRules.cpp
@@ -34,16 +34,17 @@
 #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 "StyleRule.h"
 #include "nsFont.h"
 #include "nsIURI.h"
 #include "mozAutoDocUpdate.h"
 
 using namespace mozilla;
 using namespace mozilla::dom;
 
@@ -1584,17 +1585,16 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(nsCSSFontFaceRule,
                                                   mozilla::css::Rule)
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
 // QueryInterface implementation for nsCSSFontFaceRule
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(nsCSSFontFaceRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSFontFaceRule)
-  NS_DOM_INTERFACE_MAP_ENTRY_CLASSINFO(CSSFontFaceRule)
 NS_INTERFACE_MAP_END_INHERITING(Rule)
 
 #ifdef DEBUG
 void
 nsCSSFontFaceRule::List(FILE* out, int32_t aIndent) const
 {
   nsCString baseInd, descInd;
   for (int32_t indent = aIndent; --indent >= 0; ) {
@@ -1640,16 +1640,22 @@ nsCSSFontFaceRule::GetCssTextImpl(nsAStr
   nsAutoString propText;
   mDecl.GetCssTextImpl(propText);
 
   aCssText.AssignLiteral("@font-face {\n");
   aCssText.Append(propText);
   aCssText.Append('}');
 }
 
+nsICSSDeclaration*
+nsCSSFontFaceRule::Style()
+{
+  return &mDecl;
+}
+
 NS_IMETHODIMP
 nsCSSFontFaceRule::GetStyle(nsIDOMCSSStyleDeclaration** aStyle)
 {
   NS_IF_ADDREF(*aStyle = &mDecl);
   return NS_OK;
 }
 
 // Arguably these should forward to nsCSSFontFaceStyleDecl methods.
@@ -1684,18 +1690,17 @@ nsCSSFontFaceRule::SizeOfIncludingThis(M
   // worthwhile:
   // - mDecl
 }
 
 /* virtual */ JSObject*
 nsCSSFontFaceRule::WrapObject(JSContext* aCx,
                               JS::Handle<JSObject*> aGivenProto)
 {
-  NS_NOTREACHED("We called SetIsNotDOMBinding() in our constructor");
-  return nullptr;
+  return CSSFontFaceRuleBinding::Wrap(aCx, this, aGivenProto);
 }
 
 // -----------------------------------
 // nsCSSFontFeatureValuesRule
 //
 
 /* virtual */ already_AddRefed<css::Rule>
 nsCSSFontFeatureValuesRule::Clone() const

--- a/layout/style/nsCSSRules.h
+++ b/layout/style/nsCSSRules.h
@@ -244,24 +244,22 @@ private:
 
 class nsCSSFontFaceRule final : public mozilla::css::Rule,
                                 public nsIDOMCSSFontFaceRule
 {
 public:
   nsCSSFontFaceRule(uint32_t aLineNumber, uint32_t aColumnNumber)
     : mozilla::css::Rule(aLineNumber, aColumnNumber)
   {
-    SetIsNotDOMBinding();
   }
 
   nsCSSFontFaceRule(const nsCSSFontFaceRule& aCopy)
     // copy everything except our reference count
     : mozilla::css::Rule(aCopy), mDecl(aCopy.mDecl)
   {
-    SetIsNotDOMBinding();
   }
 
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(nsCSSFontFaceRule,
                                                          mozilla::css::Rule)
 
 #ifdef DEBUG
   virtual void List(FILE* out = stdout, int32_t aIndent = 0) const override;
@@ -274,16 +272,17 @@ public:
   NS_DECL_NSIDOMCSSFONTFACERULE
 
   void SetDesc(nsCSSFontDesc aDescID, nsCSSValue const & aValue);
   void GetDesc(nsCSSFontDesc aDescID, nsCSSValue & aValue);
 
   // WebIDL interface
   uint16_t Type() const override;
   void GetCssTextImpl(nsAString& aCssText) const override;
+  nsICSSDeclaration* Style();
 
   virtual size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const override;
 
   virtual JSObject* WrapObject(JSContext* aCx,
                                JS::Handle<JSObject*> aGivenProto) override;
 
   void GetDescriptors(mozilla::CSSFontFaceDescriptors& aDescriptors) const
     { aDescriptors = mDecl.mDescriptors; }