--- a/dom/interfaces/css/moz.build
+++ b/dom/interfaces/css/moz.build
@@ -13,17 +13,16 @@ XPIDL_SOURCES += [
     'nsIDOMCSSCounterStyleRule.idl',
     'nsIDOMCSSFontFaceRule.idl',
     'nsIDOMCSSFontFeatureValuesRule.idl',
     'nsIDOMCSSGroupingRule.idl',
     'nsIDOMCSSImportRule.idl',
     'nsIDOMCSSKeyframeRule.idl',
     'nsIDOMCSSKeyframesRule.idl',
     'nsIDOMCSSMediaRule.idl',
-    'nsIDOMCSSMozDocumentRule.idl',
     'nsIDOMCSSPageRule.idl',
     'nsIDOMCSSPrimitiveValue.idl',
     'nsIDOMCSSRule.idl',
     'nsIDOMCSSRuleList.idl',
     'nsIDOMCSSStyleDeclaration.idl',
     'nsIDOMCSSStyleRule.idl',
     'nsIDOMCSSStyleSheet.idl',
     'nsIDOMCSSSupportsRule.idl',

deleted file mode 100644
--- a/dom/interfaces/css/nsIDOMCSSMozDocumentRule.idl
+++ /dev/null
@@ -1,15 +0,0 @@
-/* -*- 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/. */
-
-#include "nsIDOMCSSConditionRule.idl"
-
-/**
- * Interface for @-moz-document rules in the CSS OM.
- */
-[scriptable, uuid(2d0cef9d-c1b2-4c6c-9003-fa83040626d1)]
-interface nsIDOMCSSMozDocumentRule : nsIDOMCSSConditionRule
-{
-  // XXX Add access to the URL list.
-};

--- a/layout/style/CSSMozDocumentRule.cpp
+++ b/layout/style/CSSMozDocumentRule.cpp
@@ -14,17 +14,16 @@ using namespace mozilla::css;
 
 NS_IMPL_ADDREF_INHERITED(CSSMozDocumentRule, css::ConditionRule)
 NS_IMPL_RELEASE_INHERITED(CSSMozDocumentRule, css::ConditionRule)
 
 // QueryInterface implementation for CSSMozDocumentRule
 NS_INTERFACE_MAP_BEGIN(CSSMozDocumentRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSGroupingRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSConditionRule)
-  NS_INTERFACE_MAP_ENTRY(nsIDOMCSSMozDocumentRule)
 NS_INTERFACE_MAP_END_INHERITING(ConditionRule)
 
 // nsIDOMCSSGroupingRule methods
 NS_IMETHODIMP
 CSSMozDocumentRule::GetCssRules(nsIDOMCSSRuleList** aRuleList)
 {
   return GroupRule::GetCssRules(aRuleList);
 }

--- a/layout/style/CSSMozDocumentRule.h
+++ b/layout/style/CSSMozDocumentRule.h
@@ -4,23 +4,22 @@
  * 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_CSSMozDocumentRule_h
 #define mozilla_dom_CSSMozDocumentRule_h
 
 #include "mozilla/css/GroupRule.h"
 #include "mozilla/css/URLMatchingFunction.h"
-#include "nsIDOMCSSMozDocumentRule.h"
 
 namespace mozilla {
 namespace dom {
 
 class CSSMozDocumentRule : public css::ConditionRule
-                         , public nsIDOMCSSMozDocumentRule
+                         , public nsIDOMCSSConditionRule
 {
 protected:
   using ConditionRule::ConditionRule;
   virtual ~CSSMozDocumentRule() {}
 
 public:
   NS_DECL_ISUPPORTS_INHERITED
 
@@ -34,19 +33,16 @@ public:
                     css::URLMatchingFunction aUrlMatchingFunction);
 
   // nsIDOMCSSGroupingRule interface
   NS_DECL_NSIDOMCSSGROUPINGRULE
 
   // nsIDOMCSSConditionRule interface
   NS_IMETHOD SetConditionText(const nsAString& aConditionText) override = 0;
 
-  // nsIDOMCSSMozDocumentRule interface
-  NS_DECL_NSIDOMCSSMOZDOCUMENTRULE
-
   // WebIDL interface
   uint16_t Type() const final override {
     return nsIDOMCSSRule::DOCUMENT_RULE;
   }
   // Our XPCOM GetConditionText is OK
   void SetConditionText(const nsAString& aConditionText,
                         ErrorResult& aRv) final;
 

--- a/layout/style/GroupRule.cpp
+++ b/layout/style/GroupRule.cpp
@@ -339,17 +339,17 @@ GroupRule::AppendRulesToCssText(nsAStrin
     rule->GetCssText(cssText);
     aCssText.AppendLiteral("  ");
     aCssText.Append(cssText);
     aCssText.Append('\n');
   }
   aCssText.Append('}');
 }
 
-// nsIDOMCSSMediaRule or nsIDOMCSSMozDocumentRule methods
+// nsIDOMCSSMediaRule methods
 nsresult
 GroupRule::GetCssRules(nsIDOMCSSRuleList* *aRuleList)
 {
   NS_ADDREF(*aRuleList = CssRules());
   return NS_OK;
 }
 
 CSSRuleList*

--- a/layout/style/GroupRule.h
+++ b/layout/style/GroupRule.h
@@ -199,18 +199,17 @@ public:
   uint32_t InsertRule(const nsAString& aRule, uint32_t aIndex,
                       ErrorResult& aRv);
   void DeleteRule(uint32_t aIndex, ErrorResult& aRv);
 
 protected:
   // to help implement nsIDOMCSSRule
   void AppendRulesToCssText(nsAString& aCssText) const;
 
-  // to implement common methods on nsIDOMCSSMediaRule and
-  // nsIDOMCSSMozDocumentRule
+  // to implement methods on nsIDOMCSSMediaRule
   nsresult GetCssRules(nsIDOMCSSRuleList* *aRuleList);
   nsresult InsertRule(const nsAString & aRule, uint32_t aIndex,
                       uint32_t* _retval);
   nsresult DeleteRule(uint32_t aIndex);
 
   // Must only be called if this is a Gecko GroupRule.
   IncrementalClearCOMRuleArray& GeckoRules() {
     return mInner.as<GeckoGroupRuleRules>().mRules;

--- a/layout/style/nsCSSRules.h
+++ b/layout/style/nsCSSRules.h
@@ -27,17 +27,16 @@
 #include "mozilla/dom/CSSMozDocumentRule.h"
 #include "nsAutoPtr.h"
 #include "nsCSSPropertyID.h"
 #include "nsCSSValue.h"
 #include "nsDOMCSSDeclaration.h"
 #include "nsIDOMCSSConditionRule.h"
 #include "nsIDOMCSSFontFeatureValuesRule.h"
 #include "nsIDOMCSSGroupingRule.h"
-#include "nsIDOMCSSMozDocumentRule.h"
 #include "nsIDOMCSSSupportsRule.h"
 #include "nsTArray.h"
 
 class nsMediaList;
 
 namespace mozilla {
 
 class ErrorResult;