--- a/devtools/server/actors/object.js
+++ b/devtools/server/actors/object.js
@@ -1762,20 +1762,20 @@ DebuggerServer.ObjectActorPreviewers.Obj
     return true;
   },
 
   function ArrayLike({obj, hooks}, grip, rawObj) {
     if (isWorker || !rawObj ||
         obj.class != "DOMStringList" &&
         obj.class != "DOMTokenList" &&
         obj.class != "CSSRuleList" &&
+        obj.class != "MediaList" &&
         !(rawObj instanceof Ci.nsIDOMMozNamedAttrMap ||
           rawObj instanceof Ci.nsIDOMCSSValueList ||
           rawObj instanceof Ci.nsIDOMFileList ||
-          rawObj instanceof Ci.nsIDOMMediaList ||
           rawObj instanceof Ci.nsIDOMNodeList ||
           rawObj instanceof Ci.nsIDOMStyleSheetList)) {
       return false;
     }
 
     if (typeof rawObj.length != "number") {
       return false;
     }

--- a/dom/interfaces/base/domstubs.idl
+++ b/dom/interfaces/base/domstubs.idl
@@ -38,17 +38,16 @@ namespace dom {
 class DOMException;
 }
 }
 %}
 
 // Style Sheets
 interface nsIDOMStyleSheetList;
 interface nsIDOMStyleSheet;
-interface nsIDOMMediaList;
 
 // Base
 interface nsIDOMWindow;
 interface nsIDOMWindowCollection;
 interface nsIDOMNavigator;
 interface nsIDOMScreen;
 
 // Events

--- a/dom/interfaces/stylesheets/moz.build
+++ b/dom/interfaces/stylesheets/moz.build
@@ -3,15 +3,14 @@
 # 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/.
 
 with Files("**"):
     BUG_COMPONENT = ("Core", "DOM: CSS Object Model")
 
 XPIDL_SOURCES += [
-    'nsIDOMMediaList.idl',
     'nsIDOMStyleSheet.idl',
     'nsIDOMStyleSheetList.idl',
 ]
 
 XPIDL_MODULE = 'dom_stylesheets'
 

deleted file mode 100644
--- a/dom/interfaces/stylesheets/nsIDOMMediaList.idl
+++ /dev/null
@@ -1,28 +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 "domstubs.idl"
-
-/**
- * The nsIDOMMediaList interface is a datatype for a list of media
- * types in the Document Object Model.
- *
- * For more information on this interface please see
- * http://www.w3.org/TR/DOM-Level-2-Style
- */
-
-[uuid(9b0c2ed7-111c-4824-adf9-ef0da6dad371)]
-interface nsIDOMMediaList : nsISupports
-{
-           attribute DOMString        mediaText;
-                                        // raises(DOMException) on setting
-
-  readonly attribute unsigned long    length;
-  DOMString          item(in unsigned long index);
-  void               deleteMedium(in DOMString oldMedium)
-                                        raises(DOMException);
-  void               appendMedium(in DOMString newMedium)
-                                        raises(DOMException);
-};

--- a/dom/interfaces/stylesheets/nsIDOMStyleSheet.idl
+++ b/dom/interfaces/stylesheets/nsIDOMStyleSheet.idl
@@ -17,10 +17,9 @@
 interface nsIDOMStyleSheet : nsISupports
 {
   readonly attribute DOMString        type;
            attribute boolean          disabled;
   readonly attribute nsIDOMNode       ownerNode;
   readonly attribute nsIDOMStyleSheet parentStyleSheet;
   readonly attribute DOMString        href;
   readonly attribute DOMString        title;
-  readonly attribute nsIDOMMediaList  media;
 };

--- a/layout/style/CSSStyleSheet.cpp
+++ b/layout/style/CSSStyleSheet.cpp
@@ -20,17 +20,16 @@
 #include "nsIDocument.h"
 #include "nsPresContext.h"
 #include "nsGkAtoms.h"
 #include "nsQueryObject.h"
 #include "nsString.h"
 #include "nsStyleSet.h"
 #include "nsTArray.h"
 #include "mozilla/dom/CSSRuleList.h"
-#include "nsIDOMMediaList.h"
 #include "nsIDOMNode.h"
 #include "nsError.h"
 #include "nsCSSParser.h"
 #include "mozilla/css/Loader.h"
 #include "nsNameSpaceManager.h"
 #include "nsXMLNameSpaceMap.h"
 #include "nsCOMPtr.h"
 #include "nsContentUtils.h"

--- a/layout/style/MediaList.cpp
+++ b/layout/style/MediaList.cpp
@@ -15,17 +15,16 @@
 #include "nsCSSParser.h"
 #include "nsMediaList.h"
 
 namespace mozilla {
 namespace dom {
 
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(MediaList)
   NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
-  NS_INTERFACE_MAP_ENTRY(nsIDOMMediaList)
   NS_INTERFACE_MAP_ENTRY(nsISupports)
 NS_INTERFACE_MAP_END
 
 NS_IMPL_CYCLE_COLLECTING_ADDREF(MediaList)
 NS_IMPL_CYCLE_COLLECTING_RELEASE(MediaList)
 
 NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_0(MediaList)
 
@@ -83,55 +82,44 @@ MediaList::Create(
   }
 
   nsCSSParser parser;
   RefPtr<nsMediaList> mediaList = new nsMediaList();
   parser.ParseMediaList(aMedia, nullptr, 0, mediaList, aCallerType);
   return mediaList.forget();
 }
 
-NS_IMETHODIMP
+void
 MediaList::GetMediaText(nsAString& aMediaText)
 {
   GetText(aMediaText);
-  return NS_OK;
 }
 
-NS_IMETHODIMP
+void
 MediaList::SetMediaText(const nsAString& aMediaText)
 {
-  return DoMediaChange([&]() {
+  DoMediaChange([&]() {
     SetText(aMediaText);
     return NS_OK;
   });
 }
 
-NS_IMETHODIMP
-MediaList::GetLength(uint32_t* aLength)
-{
-  NS_ENSURE_ARG_POINTER(aLength);
-
-  *aLength = Length();
-  return NS_OK;
-}
-
-NS_IMETHODIMP
+void
 MediaList::Item(uint32_t aIndex, nsAString& aReturn)
 {
   bool dummy;
   IndexedGetter(aIndex, dummy, aReturn);
-  return NS_OK;
 }
 
-NS_IMETHODIMP
-MediaList::DeleteMedium(const nsAString& aOldMedium)
+void
+MediaList::DeleteMedium(const nsAString& aOldMedium, ErrorResult& aRv)
 {
-  return DoMediaChange([&]() { return Delete(aOldMedium); });
+  aRv = DoMediaChange([&]() { return Delete(aOldMedium); });
 }
 
-NS_IMETHODIMP
-MediaList::AppendMedium(const nsAString& aNewMedium)
+void
+MediaList::AppendMedium(const nsAString& aNewMedium, ErrorResult& aRv)
 {
-  return DoMediaChange([&]() { return Append(aNewMedium); });
+  aRv = DoMediaChange([&]() { return Append(aNewMedium); });
 }
 
 } // namespace dom
 } // namespace mozilla

--- a/layout/style/MediaList.h
+++ b/layout/style/MediaList.h
@@ -8,17 +8,16 @@
 
 #ifndef mozilla_dom_MediaList_h
 #define mozilla_dom_MediaList_h
 
 #include "mozilla/ErrorResult.h"
 #include "mozilla/ServoUtils.h"
 #include "mozilla/StyleBackendType.h"
 
-#include "nsIDOMMediaList.h"
 #include "nsWrapperCache.h"
 
 class nsIDocument;
 class nsPresContext;
 class nsMediaQueryResultCacheKey;
 
 namespace mozilla {
 class StyleSheet;
@@ -28,17 +27,17 @@ namespace dom {
 // XXX This class doesn't use the branch dispatch approach that we use
 //     elsewhere for stylo, but instead just relies on virtual call.
 //     That's because this class should not be critical to performance,
 //     and using branch dispatch would make it much more complicated.
 //     Performance critical path should hold a subclass of this class
 //     directly. We may want to determine in the future whether the
 //     above is correct.
 
-class MediaList : public nsIDOMMediaList
+class MediaList : public nsISupports
                 , public nsWrapperCache
 {
 public:
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS
   NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(MediaList)
 
   /**
    * Creates a MediaList backed by the given StyleBackendType.
@@ -58,32 +57,25 @@ public:
   virtual bool Matches(nsPresContext* aPresContext) const = 0;
 
 #ifdef DEBUG
   virtual bool IsServo() const = 0;
 #endif
 
   void SetStyleSheet(StyleSheet* aSheet);
 
-  NS_DECL_NSIDOMMEDIALIST
-
   // WebIDL
-  // XPCOM GetMediaText and SetMediaText are fine.
+  void GetMediaText(nsAString& aMediaText);
+  void SetMediaText(const nsAString& aMediaText);
   virtual uint32_t Length() = 0;
   virtual void IndexedGetter(uint32_t aIndex, bool& aFound,
                              nsAString& aReturn) = 0;
-  // XPCOM Item is fine.
-  void DeleteMedium(const nsAString& aMedium, ErrorResult& aRv)
-  {
-    aRv = DeleteMedium(aMedium);
-  }
-  void AppendMedium(const nsAString& aMedium, ErrorResult& aRv)
-  {
-    aRv = AppendMedium(aMedium);
-  }
+  void Item(uint32_t aIndex, nsAString& aResult);
+  void DeleteMedium(const nsAString& aMedium, ErrorResult& aRv);
+  void AppendMedium(const nsAString& aMedium, ErrorResult& aRv);
 
 protected:
   virtual nsresult Delete(const nsAString& aOldMedium) = 0;
   virtual nsresult Append(const nsAString& aNewMedium) = 0;
 
   virtual ~MediaList() {
     MOZ_ASSERT(!mStyleSheet, "Backpointer should have been cleared");
   }

--- a/layout/style/ServoMediaRule.cpp
+++ b/layout/style/ServoMediaRule.cpp
@@ -96,17 +96,17 @@ ServoMediaRule::GetConditionText(nsAStri
 {
   Media()->GetMediaText(aConditionText);
 }
 
 void
 ServoMediaRule::SetConditionText(const nsAString& aConditionText,
                                  ErrorResult& aRv)
 {
-  aRv = Media()->SetMediaText(aConditionText);
+  Media()->SetMediaText(aConditionText);
 }
 
 /* virtual */ void
 ServoMediaRule::GetCssTextImpl(nsAString& aCssText) const
 {
   Servo_MediaRule_GetCssText(mRawRule, &aCssText);
 }
 

--- a/layout/style/StyleSheet.cpp
+++ b/layout/style/StyleSheet.cpp
@@ -372,23 +372,16 @@ StyleSheet::GetTitle(nsAString& aTitle)
 NS_IMETHODIMP
 StyleSheet::GetParentStyleSheet(nsIDOMStyleSheet** aParentStyleSheet)
 {
   NS_ENSURE_ARG_POINTER(aParentStyleSheet);
   NS_IF_ADDREF(*aParentStyleSheet = GetParentStyleSheet());
   return NS_OK;
 }
 
-NS_IMETHODIMP
-StyleSheet::GetMedia(nsIDOMMediaList** aMedia)
-{
-  NS_ADDREF(*aMedia = Media());
-  return NS_OK;
-}
-
 void
 StyleSheet::WillDirty()
 {
   if (mInner->mComplete) {
     EnsureUniqueInner();
   }
 }
 

--- a/layout/style/StyleSheet.h
+++ b/layout/style/StyleSheet.h
@@ -240,17 +240,16 @@ public:
   // nsIDOMStyleSheet interface
   NS_IMETHOD GetType(nsAString& aType) final;
   NS_IMETHOD GetDisabled(bool* aDisabled) final;
   NS_IMETHOD SetDisabled(bool aDisabled) final;
   NS_IMETHOD GetOwnerNode(nsIDOMNode** aOwnerNode) final;
   NS_IMETHOD GetParentStyleSheet(nsIDOMStyleSheet** aParentStyleSheet) final;
   NS_IMETHOD GetHref(nsAString& aHref) final;
   NS_IMETHOD GetTitle(nsAString& aTitle) final;
-  NS_IMETHOD GetMedia(nsIDOMMediaList** aMedia) final;
 
   // Changes to sheets should be inside of a WillDirty-DidDirty pair.
   // However, the calls do not need to be matched; it's ok to call
   // WillDirty and then make no change and skip the DidDirty call.
   void WillDirty();
   virtual void DidDirty() {}
 
   // Called when a rule changes from CSSOM.

--- a/layout/style/nsCSSRules.cpp
+++ b/layout/style/nsCSSRules.cpp
@@ -328,28 +328,21 @@ MediaRule::GetConditionText(nsAString& a
   AppendConditionText(aConditionText);
 }
 
 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;
+    mMedia = new nsMediaList();
+    mMedia->SetStyleSheet(GetStyleSheet());
   }
 
-  aRv = mMedia->SetMediaText(aConditionText);
+  mMedia->SetMediaText(aConditionText);
 }
 
 // GroupRule interface
 /* virtual */ bool
 MediaRule::UseForPresentation(nsPresContext* aPresContext,
                               nsMediaQueryResultCacheKey& aKey)
 {
   if (mMedia) {

--- a/xpcom/reflect/xptinfo/ShimInterfaceInfo.cpp
+++ b/xpcom/reflect/xptinfo/ShimInterfaceInfo.cpp
@@ -45,17 +45,16 @@
 #include "nsIDOMGeoPositionError.h"
 #include "nsIDOMHistory.h"
 #include "nsIDOMHTMLDocument.h"
 #include "nsIDOMHTMLElement.h"
 #include "nsIDOMHTMLFormElement.h"
 #include "nsIDOMHTMLInputElement.h"
 #include "nsIDOMHTMLMediaElement.h"
 #include "nsIDOMKeyEvent.h"
-#include "nsIDOMMediaList.h"
 #include "nsIDOMMouseEvent.h"
 #include "nsIDOMMouseScrollEvent.h"
 #include "nsIDOMMutationEvent.h"
 #include "nsIDOMMozNamedAttrMap.h"
 #include "nsIDOMNode.h"
 #include "nsIDOMNodeIterator.h"
 #include "nsIDOMNodeList.h"
 #include "nsIDOMNotifyPaintEvent.h"
@@ -290,17 +289,16 @@ const ComponentsInterfaceShimEntry kComp
   DEFINE_SHIM(History),
   DEFINE_SHIM(HTMLDocument),
   DEFINE_SHIM(HTMLElement),
   DEFINE_SHIM(HTMLFormElement),
   DEFINE_SHIM(HTMLInputElement),
   DEFINE_SHIM(HTMLMediaElement),
   DEFINE_SHIM(KeyEvent),
   DEFINE_SHIM_WITH_CUSTOM_INTERFACE(nsIListBoxObject, ListBoxObject),
-  DEFINE_SHIM(MediaList),
   DEFINE_SHIM_WITH_CUSTOM_INTERFACE(nsIMenuBoxObject, MenuBoxObject),
   DEFINE_SHIM(MouseEvent),
   DEFINE_SHIM(MouseScrollEvent),
   DEFINE_SHIM(MutationEvent),
   DEFINE_SHIM_WITH_CUSTOM_INTERFACE(nsIDOMMozNamedAttrMap, NamedNodeMap),
   DEFINE_SHIM(NodeIterator),
   DEFINE_SHIM(NodeList),
   DEFINE_SHIM(Node),