--- a/dom/base/nsGkAtomList.h
+++ b/dom/base/nsGkAtomList.h
@@ -2448,8 +2448,18 @@ GK_ATOM(nsuri_xml, "http://www.w3.org/XM
 GK_ATOM(nsuri_xhtml, "http://www.w3.org/1999/xhtml")
 GK_ATOM(nsuri_xlink, "http://www.w3.org/1999/xlink")
 GK_ATOM(nsuri_xslt, "http://www.w3.org/1999/XSL/Transform")
 GK_ATOM(nsuri_xbl, "http://www.mozilla.org/xbl")
 GK_ATOM(nsuri_mathml, "http://www.w3.org/1998/Math/MathML")
 GK_ATOM(nsuri_rdf, "http://www.w3.org/1999/02/22-rdf-syntax-ns#")
 GK_ATOM(nsuri_xul, "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul")
 GK_ATOM(nsuri_svg, "http://www.w3.org/2000/svg")
+
+// MSE
+GK_ATOM(onsourceopen, "onsourceopen")
+GK_ATOM(onsourceended, "onsourceended")
+GK_ATOM(onsourceclosed, "onsourceclosed")
+GK_ATOM(onupdatestart, "onupdatestart")
+GK_ATOM(onupdate, "onupdate")
+GK_ATOM(onupdateend, "onupdateend")
+GK_ATOM(onaddsourcebuffer, "onaddsourcebuffer")
+GK_ATOM(onremovesourcebuffer, "onremovesourcebuffer")

--- a/dom/media/mediasource/MediaSource.h
+++ b/dom/media/mediasource/MediaSource.h
@@ -67,16 +67,21 @@ public:
   void EndOfStream(const Optional<MediaSourceEndOfStreamError>& aError, ErrorResult& aRv);
 
   void SetLiveSeekableRange(double aStart, double aEnd, ErrorResult& aRv);
   void ClearLiveSeekableRange(ErrorResult& aRv);
 
   static bool IsTypeSupported(const GlobalObject&, const nsAString& aType);
 
   static bool Enabled(JSContext* cx, JSObject* aGlobal);
+
+  IMPL_EVENT_HANDLER(sourceopen);
+  IMPL_EVENT_HANDLER(sourceended);
+  IMPL_EVENT_HANDLER(sourceclosed);
+
   /** End WebIDL Methods. */
 
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(MediaSource, DOMEventTargetHelper)
   NS_DECLARE_STATIC_IID_ACCESSOR(MOZILLA_DOM_MEDIASOURCE_IMPLEMENTATION_IID)
 
   nsPIDOMWindowInner* GetParentObject() const;
 

--- a/dom/media/mediasource/SourceBuffer.h
+++ b/dom/media/mediasource/SourceBuffer.h
@@ -82,16 +82,23 @@ public:
 
   void AppendBuffer(const ArrayBuffer& aData, ErrorResult& aRv);
   void AppendBuffer(const ArrayBufferView& aData, ErrorResult& aRv);
 
   void Abort(ErrorResult& aRv);
   void AbortBufferAppend();
 
   void Remove(double aStart, double aEnd, ErrorResult& aRv);
+
+  IMPL_EVENT_HANDLER(updatestart);
+  IMPL_EVENT_HANDLER(update);
+  IMPL_EVENT_HANDLER(updateend);
+  IMPL_EVENT_HANDLER(error);
+  IMPL_EVENT_HANDLER(abort);
+
   /** End WebIDL Methods. */
 
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(SourceBuffer, DOMEventTargetHelper)
 
   SourceBuffer(MediaSource* aMediaSource, const nsACString& aType);
 
   MediaSource* GetParentObject() const;

--- a/dom/media/mediasource/SourceBufferList.h
+++ b/dom/media/mediasource/SourceBufferList.h
@@ -30,16 +30,20 @@ class MediaSource;
 
 class SourceBufferList final : public DOMEventTargetHelper
 {
 public:
   /** WebIDL Methods. */
   SourceBuffer* IndexedGetter(uint32_t aIndex, bool& aFound);
 
   uint32_t Length();
+
+  IMPL_EVENT_HANDLER(addsourcebuffer);
+  IMPL_EVENT_HANDLER(removesourcebuffer);
+
   /** End WebIDL methods. */
 
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(SourceBufferList,
                                            DOMEventTargetHelper)
 
   explicit SourceBufferList(MediaSource* aMediaSource);
 

--- a/dom/webidl/MediaSource.webidl
+++ b/dom/webidl/MediaSource.webidl
@@ -23,16 +23,19 @@ enum MediaSourceEndOfStreamError {
 
 [Constructor, Func="mozilla::dom::MediaSource::Enabled"]
 interface MediaSource : EventTarget {
   readonly attribute SourceBufferList sourceBuffers;
   readonly attribute SourceBufferList activeSourceBuffers;
   readonly attribute MediaSourceReadyState readyState;
   [SetterThrows]
   attribute unrestricted double duration;
+  attribute EventHandler onsourceopen;
+  attribute EventHandler onsourceended;
+  attribute EventHandler onsourceclosed;
   [NewObject, Throws]
   SourceBuffer addSourceBuffer(DOMString type);
   [Throws]
   void removeSourceBuffer(SourceBuffer sourceBuffer);
   [Throws]
   void endOfStream(optional MediaSourceEndOfStreamError error);
   [Throws]
   void setLiveSeekableRange(double start, double end);

--- a/dom/webidl/SourceBuffer.webidl
+++ b/dom/webidl/SourceBuffer.webidl
@@ -26,16 +26,21 @@ interface SourceBuffer : EventTarget {
   attribute double timestampOffset;
   //readonly attribute AudioTrackList audioTracks;
   //readonly attribute VideoTrackList videoTracks;
   //readonly attribute TextTrackList textTracks;
   [SetterThrows]
   attribute double appendWindowStart;
   [SetterThrows]
   attribute unrestricted double appendWindowEnd;
+  attribute EventHandler onupdatestart;
+  attribute EventHandler onupdate;
+  attribute EventHandler onupdateend;
+  attribute EventHandler onerror;
+  attribute EventHandler onabort;
   [Throws]
   void appendBuffer(ArrayBuffer data);
   [Throws]
   void appendBuffer(ArrayBufferView data);
   //[Throws]
   //void appendStream(Stream stream, [EnforceRange] optional unsigned long long maxSize);
   [Throws]
   void abort();

--- a/dom/webidl/SourceBufferList.webidl
+++ b/dom/webidl/SourceBufferList.webidl
@@ -8,10 +8,12 @@
  *
  * Copyright © 2012 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C
  * liability, trademark and document use rules apply.
  */
 
 [Func="mozilla::dom::MediaSource::Enabled"]
 interface SourceBufferList : EventTarget {
   readonly attribute unsigned long length;
+  attribute EventHandler onaddsourcebuffer;
+  attribute EventHandler onremovesourcebuffer;
   getter SourceBuffer (unsigned long index);
 };