diff --git a/dom/bindings/Bindings.conf b/dom/bindings/Bindings.conf
index 26751ac8c6..33c812a542 100644
--- a/dom/bindings/Bindings.conf
+++ b/dom/bindings/Bindings.conf
@@ -205,6 +205,11 @@ DOMInterfaces = {
     'nativeType': 'nsROCSSPrimitiveValue',
 },
 
+'CSSRule': {
+#    'hasXPConnectImpls': True,
+    'nativeType': 'mozilla::css::Rule'
+},
+
 'CSSStyleDeclaration': {
     'nativeType': 'nsICSSDeclaration'
 },
@@ -1689,7 +1694,6 @@ def addExternalIface(iface, nativeType=None, headerFile=None,
 
 addExternalIface('ApplicationCache', nativeType='nsIDOMOfflineResourceList')
 addExternalIface('Counter')
-addExternalIface('CSSRule')
 addExternalIface('RTCDataChannel', nativeType='nsIDOMDataChannel')
 addExternalIface('HitRegionOptions', nativeType='nsISupports')
 addExternalIface('imgINotificationObserver', nativeType='imgINotificationObserver')
diff --git a/dom/webidl/CSSRule.webidl b/dom/webidl/CSSRule.webidl
new file mode 100644
index 0000000000..6c4dac2e62
--- /dev/null
+++ b/dom/webidl/CSSRule.webidl
@@ -0,0 +1,52 @@
+/* -*- 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/cssom/#the-cssrule-interface
+ * https://drafts.csswg.org/css-animations/#interface-cssrule
+ * https://drafts.csswg.org/css-counter-styles-3/#extentions-to-cssrule-interface
+ * https://drafts.csswg.org/css-conditional-3/#extentions-to-cssrule-interface
+ * https://drafts.csswg.org/css-fonts-3/#om-fontfeaturevalues
+ */
+
+// https://drafts.csswg.org/cssom/#the-cssrule-interface
+interface CSSRule {
+
+  const unsigned short STYLE_RULE = 1;
+  const unsigned short CHARSET_RULE = 2; // historical
+  const unsigned short IMPORT_RULE = 3;
+  const unsigned short MEDIA_RULE = 4;
+  const unsigned short FONT_FACE_RULE = 5;
+  const unsigned short PAGE_RULE = 6;
+  // FIXME: We don't support MARGIN_RULE yet.
+  // XXXbz Should we expose the constant anyway?
+  // const unsigned short MARGIN_RULE = 9;
+  const unsigned short NAMESPACE_RULE = 10;
+  readonly attribute unsigned short type;
+  attribute DOMString cssText;
+  readonly attribute CSSRule? parentRule;
+  readonly attribute CSSStyleSheet? parentStyleSheet;
+};
+
+// https://drafts.csswg.org/css-animations/#interface-cssrule
+partial interface CSSRule {
+    const unsigned short KEYFRAMES_RULE = 7;
+    const unsigned short KEYFRAME_RULE = 8;
+};
+
+// https://drafts.csswg.org/css-counter-styles-3/#extentions-to-cssrule-interface
+partial interface CSSRule {
+    const unsigned short COUNTER_STYLE_RULE = 11;
+};
+
+// https://drafts.csswg.org/css-conditional-3/#extentions-to-cssrule-interface
+partial interface CSSRule {
+    const unsigned short SUPPORTS_RULE = 12;
+};
+
+// https://drafts.csswg.org/css-fonts-3/#om-fontfeaturevalues
+partial interface CSSRule {
+  const unsigned short FONT_FEATURE_VALUES_RULE = 14;
+};
diff --git a/dom/webidl/CSSStyleDeclaration.webidl b/dom/webidl/CSSStyleDeclaration.webidl
index 561e5cce1b..b672c0dd31 100644
--- a/dom/webidl/CSSStyleDeclaration.webidl
+++ b/dom/webidl/CSSStyleDeclaration.webidl
@@ -7,8 +7,6 @@
  * http://dev.w3.org/csswg/cssom/
  */
 
-interface CSSRule;
-
 interface CSSStyleDeclaration {
   [CEReactions, SetterThrows]
   attribute DOMString cssText;
diff --git a/dom/webidl/CSSStyleSheet.webidl b/dom/webidl/CSSStyleSheet.webidl
index 677d3ec528..45ef840208 100644
--- a/dom/webidl/CSSStyleSheet.webidl
+++ b/dom/webidl/CSSStyleSheet.webidl
@@ -7,8 +7,6 @@
  * http://dev.w3.org/csswg/cssom/
  */
 
-interface CSSRule;
-
 enum CSSStyleSheetParsingMode {
   "author",
   "user",
diff --git a/dom/webidl/StyleRuleChangeEvent.webidl b/dom/webidl/StyleRuleChangeEvent.webidl
index 0b783366ba..ef35bae648 100644
--- a/dom/webidl/StyleRuleChangeEvent.webidl
+++ b/dom/webidl/StyleRuleChangeEvent.webidl
@@ -3,8 +3,6 @@
  * 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/.
  */
-interface CSSRule;
-
 [ChromeOnly, Constructor(DOMString type, optional StyleRuleChangeEventInit eventInitDict)]
 interface StyleRuleChangeEvent : Event
 {
diff --git a/dom/webidl/StyleSheet.webidl b/dom/webidl/StyleSheet.webidl
index 71a8ccd8f4..26c2fbb999 100644
--- a/dom/webidl/StyleSheet.webidl
+++ b/dom/webidl/StyleSheet.webidl
@@ -7,8 +7,6 @@
  * http://dev.w3.org/csswg/cssom/
  */
 
-interface CSSRule;
-
 interface StyleSheet {
   [Constant]
   readonly attribute DOMString type;
diff --git a/dom/webidl/moz.build b/dom/webidl/moz.build
index e7cc11cecc..904d299540 100644
--- a/dom/webidl/moz.build
+++ b/dom/webidl/moz.build
@@ -93,6 +93,7 @@ WEBIDL_FILES = [
     'CSSLexer.webidl',
     'CSSPrimitiveValue.webidl',
     'CSSPseudoElement.webidl',
+    'CSSRule.webidl',
     'CSSRuleList.webidl',
     'CSSStyleDeclaration.webidl',
     'CSSStyleSheet.webidl',
diff --git a/layout/style/CSSRuleList.h b/layout/style/CSSRuleList.h
index 786cc1b884..60ceec0db9 100644
--- a/layout/style/CSSRuleList.h
+++ b/layout/style/CSSRuleList.h
@@ -7,6 +7,7 @@
 #define mozilla_dom_CSSRuleList_h
 
 #include "mozilla/StyleSheetInlines.h"
+#include "mozilla/css/Rule.h"
 #include "nsIDOMCSSRule.h"
 #include "nsIDOMCSSRuleList.h"
 #include "nsWrapperCache.h"
@@ -45,13 +46,13 @@ public:
   }
 
   // WebIDL API
-  nsIDOMCSSRule* Item(uint32_t aIndex)
+  css::Rule* Item(uint32_t aIndex)
   {
     bool unused;
     return IndexedGetter(aIndex, unused);
   }
 
-  virtual nsIDOMCSSRule* IndexedGetter(uint32_t aIndex, bool& aFound) = 0;
+  virtual css::Rule* IndexedGetter(uint32_t aIndex, bool& aFound) = 0;
   virtual uint32_t Length() = 0;
 
 protected:
diff --git a/layout/style/CSSStyleSheet.cpp b/layout/style/CSSStyleSheet.cpp
index 1a3944fdb4..1307864c9d 100644
--- a/layout/style/CSSStyleSheet.cpp
+++ b/layout/style/CSSStyleSheet.cpp
@@ -61,7 +61,7 @@ public:
 
   virtual CSSStyleSheet* GetParentObject() override;
 
-  virtual nsIDOMCSSRule*
+  virtual css::Rule*
   IndexedGetter(uint32_t aIndex, bool& aFound) override;
   virtual uint32_t
   Length() override;
@@ -101,7 +101,7 @@ CSSRuleListImpl::Length()
   return AssertedCast<uint32_t>(mStyleSheet->StyleRuleCount());
 }
 
-nsIDOMCSSRule*    
+css::Rule*
 CSSRuleListImpl::IndexedGetter(uint32_t aIndex, bool& aFound)
 {
   aFound = false;
@@ -1648,7 +1648,7 @@ CSSStyleSheet::Media()
   return mMedia;
 }
 
-nsIDOMCSSRule*
+css::Rule*
 CSSStyleSheet::GetDOMOwnerRule() const
 {
   return mOwnerRule;
diff --git a/layout/style/CSSStyleSheet.h b/layout/style/CSSStyleSheet.h
index 69028dcdc8..640a05340f 100644
--- a/layout/style/CSSStyleSheet.h
+++ b/layout/style/CSSStyleSheet.h
@@ -212,7 +212,7 @@ public:
   // 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;
+  css::Rule* GetDOMOwnerRule() const final;
 
   void WillDirty();
   void DidDirty();
diff --git a/layout/style/Rule.h b/layout/style/Rule.h
index 00082c1e2c..ea6ca79f29 100644
--- a/layout/style/Rule.h
+++ b/layout/style/Rule.h
@@ -118,6 +118,11 @@ public:
   // WebIDL interface, aka helpers for nsIDOMCSSRule implementation.
   virtual uint16_t Type() const = 0;
   virtual void GetCssTextImpl(nsAString& aCssText) const = 0;
+  // XPCOM GetCssText is OK, since it never throws.
+  // XPCOM SetCssText is OK, since it never throws.
+  Rule* GetParentRule() const;
+  StyleSheet* GetParentStyleSheet() const { return GetStyleSheet(); }
+  nsIDocument* GetParentObject() const { return GetDocument(); }
 
 protected:
   // True if we're known-live for cycle collection purposes.
@@ -137,4 +142,18 @@ protected:
 } // namespace css
 } // namespace mozilla
 
+// Specialization of the bindings UnwrapArg setup for css::Rule, so we can avoid
+// adding an IID to css::Rule.  This can go away once all css::Rule subclasses
+// are on WebIDL bindings.
+
+#include "js/TypeDecls.h"
+
+namespace mozilla {
+namespace dom {
+template <>
+nsresult
+UnwrapArg(JS::Handle<JSObject*> src, css::Rule** ppArg);
+} // namepace dom
+} // namespace mozilla
+
 #endif /* mozilla_css_Rule_h___ */
diff --git a/layout/style/StyleSheet.h b/layout/style/StyleSheet.h
index bbd455a02b..fd1e9b3652 100644
--- a/layout/style/StyleSheet.h
+++ b/layout/style/StyleSheet.h
@@ -29,6 +29,10 @@ class CSSRuleList;
 class SRIMetadata;
 } // namespace dom
 
+namespace css {
+class Rule;
+}
+
 /**
  * Superclass for CSSStyleSheet.
  */
@@ -145,7 +149,7 @@ public:
   // The XPCOM SetDisabled is fine for WebIDL.
 
   // WebIDL CSSStyleSheet API
-  virtual nsIDOMCSSRule* GetDOMOwnerRule() const = 0;
+  virtual css::Rule* GetDOMOwnerRule() const = 0;
   dom::CSSRuleList* GetCssRules(nsIPrincipal& aSubjectPrincipal,
                                 ErrorResult& aRv);
   uint32_t InsertRule(const nsAString& aRule, uint32_t aIndex,
diff --git a/layout/style/nsCSSRules.cpp b/layout/style/nsCSSRules.cpp
index ff0b33eb25..e30cddc03e 100644
--- a/layout/style/nsCSSRules.cpp
+++ b/layout/style/nsCSSRules.cpp
@@ -45,6 +45,27 @@ using namespace mozilla::dom;
 
 // base class for all rule types in a CSS style sheet
 
+// Temporary code that can go away once all css::Rules are on WebIDL bindings.
+#include "xpcpublic.h"
+namespace mozilla {
+namespace dom {
+template<>
+nsresult
+UnwrapArg(JS::Handle<JSObject*> src, css::Rule** ppArg)
+{
+  MOZ_ASSERT(NS_IsMainThread());
+  nsCOMPtr<nsIDOMCSSRule> rule =
+    do_QueryInterface(xpc::UnwrapReflectorToISupports(src));
+  if (!rule) {
+    return NS_NOINTERFACE;
+  }
+  *ppArg = rule->GetCSSRule();
+  NS_ADDREF(*ppArg);
+  return NS_OK;
+}
+} // namespace dom
+} // namespace mozilla
+
 namespace mozilla {
 namespace css {
 
@@ -153,6 +174,12 @@ Rule::GetCssText(nsAString& aCssText)
   return NS_OK;
 }
 
+Rule*
+Rule::GetParentRule() const
+{
+  return mParentRule;
+}
+
 // -------------------------------
 // Style Rule List for group rules
 //
@@ -164,7 +191,7 @@ public:
 
   virtual CSSStyleSheet* GetParentObject() override;
 
-  virtual nsIDOMCSSRule*
+  virtual Rule*
   IndexedGetter(uint32_t aIndex, bool& aFound) override;
   virtual uint32_t
   Length() override;
@@ -209,7 +236,7 @@ GroupRuleRuleList::Length()
   return AssertedCast<uint32_t>(mGroupRule->StyleRuleCount());
 }
 
-nsIDOMCSSRule*
+Rule*
 GroupRuleRuleList::IndexedGetter(uint32_t aIndex, bool& aFound)
 {
   aFound = false;