--- a/dom/html/HTMLMediaElement.cpp
+++ b/dom/html/HTMLMediaElement.cpp
@@ -5,16 +5,17 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "mozilla/dom/HTMLMediaElement.h"
 #include "mozilla/dom/HTMLMediaElementBinding.h"
 #include "mozilla/dom/HTMLSourceElement.h"
 #include "mozilla/dom/HTMLAudioElement.h"
 #include "mozilla/dom/HTMLVideoElement.h"
 #include "mozilla/dom/ElementInlines.h"
+#include "mozilla/dom/PlayPromise.h"
 #include "mozilla/dom/Promise.h"
 #include "mozilla/ArrayUtils.h"
 #include "mozilla/NotNull.h"
 #include "mozilla/MathAlgorithms.h"
 #include "mozilla/AsyncEventDispatcher.h"
 #include "mozilla/dom/MediaEncryptedEvent.h"
 #include "mozilla/EMEUtils.h"
 #include "mozilla/EventDispatcher.h"
@@ -119,17 +120,17 @@
 #include <cmath>
 #ifdef XP_WIN
 #include "objbase.h"
 // Some Windows header defines this, so undef it as it conflicts with our
 // function of the same name.
 #undef GetCurrentTime
 #endif
 
-static mozilla::LazyLogModule gMediaElementLog("nsMediaElement");
+mozilla::LazyLogModule gMediaElementLog("nsMediaElement");
 static mozilla::LazyLogModule gMediaElementEventsLog("nsMediaElementEvents");
 
 #define LOG(type, msg) MOZ_LOG(gMediaElementLog, type, msg)
 #define LOG_EVENT(type, msg) MOZ_LOG(gMediaElementEventsLog, type, msg)
 
 #include "nsIContentSecurityPolicy.h"
 
 #include "mozilla/Preferences.h"
@@ -177,25 +178,25 @@ static const double THRESHOLD_LOW_PLAYBA
 
 // Media error values.  These need to match the ones in MediaError.webidl.
 static const unsigned short MEDIA_ERR_ABORTED = 1;
 static const unsigned short MEDIA_ERR_NETWORK = 2;
 static const unsigned short MEDIA_ERR_DECODE = 3;
 static const unsigned short MEDIA_ERR_SRC_NOT_SUPPORTED = 4;
 
 static void
-ResolvePromisesWithUndefined(const nsTArray<RefPtr<Promise>>& aPromises)
+ResolvePromisesWithUndefined(const nsTArray<RefPtr<PlayPromise>>& aPromises)
 {
   for (auto& promise : aPromises) {
     promise->MaybeResolveWithUndefined();
   }
 }
 
 static void
-RejectPromises(const nsTArray<RefPtr<Promise>>& aPromises, nsresult aError)
+RejectPromises(const nsTArray<RefPtr<PlayPromise>>& aPromises, nsresult aError)
 {
   for (auto& promise : aPromises) {
     promise->MaybeReject(aError);
   }
 }
 
 // Under certain conditions there may be no-one holding references to
 // a media element from script, DOM parent, etc, but the element may still
@@ -296,26 +297,29 @@ public:
  *
  * The constructor appends the constructed instance into the passed media
  * element's mPendingPlayPromisesRunners member and once the the runner is run
  * (whether fulfilled or canceled), it removes itself from
  * mPendingPlayPromisesRunners.
  */
 class HTMLMediaElement::nsResolveOrRejectPendingPlayPromisesRunner : public nsMediaEvent
 {
-  nsTArray<RefPtr<Promise>> mPromises;
+  nsTArray<RefPtr<PlayPromise>> mPromises;
   nsresult mError;
 
 public:
-  nsResolveOrRejectPendingPlayPromisesRunner(HTMLMediaElement* aElement,
-                                             nsTArray<RefPtr<Promise>>&& aPromises,
-                                             nsresult aError = NS_OK)
-  : nsMediaEvent("HTMLMediaElement::nsResolveOrRejectPendingPlayPromisesRunner", aElement)
-  , mPromises(Move(aPromises))
-  , mError(aError)
+  nsResolveOrRejectPendingPlayPromisesRunner(
+    HTMLMediaElement* aElement,
+    nsTArray<RefPtr<PlayPromise>>&& aPromises,
+    nsresult aError = NS_OK)
+    : nsMediaEvent(
+        "HTMLMediaElement::nsResolveOrRejectPendingPlayPromisesRunner",
+        aElement)
+    , mPromises(Move(aPromises))
+    , mError(aError)
   {
     mElement->mPendingPlayPromisesRunners.AppendElement(this);
   }
 
   void ResolveOrReject()
   {
     if (NS_SUCCEEDED(mError)) {
       ResolvePromisesWithUndefined(mPromises);
@@ -333,20 +337,21 @@ public:
     mElement->mPendingPlayPromisesRunners.RemoveElement(this);
     return NS_OK;
   }
 };
 
 class HTMLMediaElement::nsNotifyAboutPlayingRunner : public nsResolveOrRejectPendingPlayPromisesRunner
 {
 public:
-  nsNotifyAboutPlayingRunner(HTMLMediaElement* aElement,
-                             nsTArray<RefPtr<Promise>>&& aPendingPlayPromises)
-  : nsResolveOrRejectPendingPlayPromisesRunner(aElement,
-                                               Move(aPendingPlayPromises))
+  nsNotifyAboutPlayingRunner(
+    HTMLMediaElement* aElement,
+    nsTArray<RefPtr<PlayPromise>>&& aPendingPlayPromises)
+    : nsResolveOrRejectPendingPlayPromisesRunner(aElement,
+                                                 Move(aPendingPlayPromises))
   {
   }
 
   NS_IMETHOD Run() override
   {
     if (IsCancelled()) {
       mElement->mPendingPlayPromisesRunners.RemoveElement(this);
       return NS_OK;
@@ -3960,17 +3965,17 @@ HTMLMediaElement::Play(ErrorResult& aRv)
   LOG(LogLevel::Debug, ("%p Play() called by JS readyState=%d", this, mReadyState));
 
   if (mAudioChannelWrapper && mAudioChannelWrapper->IsPlaybackBlocked()) {
     MaybeDoLoad();
 
     // A blocked media element will be resumed later, so we return a pending
     // promise which might be resolved/rejected depends on the result of
     // resuming the blocked media element.
-    RefPtr<Promise> promise = CreateDOMPromise(aRv);
+    RefPtr<PlayPromise> promise = CreatePlayPromise(aRv);
 
     if (NS_WARN_IF(aRv.Failed())) {
       return nullptr;
     }
 
     LOG(LogLevel::Debug, ("%p Play() call delayed by AudioChannelAgent", this));
 
     mPendingPlayPromises.AppendElement(promise);
@@ -3984,54 +3989,56 @@ HTMLMediaElement::Play(ErrorResult& aRv)
   return promise.forget();
 }
 
 already_AddRefed<Promise>
 HTMLMediaElement::PlayInternal(ErrorResult& aRv)
 {
   MOZ_ASSERT(!aRv.Failed());
 
+  RefPtr<PlayPromise> promise = CreatePlayPromise(aRv);
+
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
   // 4.8.12.8
   // When the play() method on a media element is invoked, the user agent must
   // run the following steps.
 
   // 4.8.12.8 - Step 1:
   // If the media element is not allowed to play, return a promise rejected
   // with a "NotAllowedError" DOMException and abort these steps.
   // Note: IsAllowedToPlay() needs to know whether there is an audio track
   // in the resource, and for that we need to be at readyState HAVE_METADATA
   // or above. So only reject here if we're at readyState HAVE_METADATA. If
   // we're below that, we'll we delay fulfilling the play promise until we've
   // reached readyState >= HAVE_METADATA below.
   if (mReadyState >= HAVE_METADATA && !IsAllowedToPlay()) {
     // NOTE: for promise-based-play, will return a rejected promise here.
     LOG(LogLevel::Debug,
         ("%p Play() promise rejected because not allowed to play.", this));
-    aRv.Throw(NS_ERROR_DOM_MEDIA_NOT_ALLOWED_ERR);
-    return nullptr;
+    promise->MaybeReject(NS_ERROR_DOM_MEDIA_NOT_ALLOWED_ERR);
+    return promise.forget();
   }
 
   // 4.8.12.8 - Step 2:
   // If the media element's error attribute is not null and its code
   // attribute has the value MEDIA_ERR_SRC_NOT_SUPPORTED, return a promise
   // rejected with a "NotSupportedError" DOMException and abort these steps.
   if (GetError() && GetError()->Code() == MEDIA_ERR_SRC_NOT_SUPPORTED) {
     LOG(LogLevel::Debug,
         ("%p Play() promise rejected because source not supported.", this));
-    aRv.Throw(NS_ERROR_DOM_MEDIA_NOT_SUPPORTED_ERR);
-    return nullptr;
+    promise->MaybeReject(NS_ERROR_DOM_MEDIA_NOT_SUPPORTED_ERR);
+    return promise.forget();
   }
 
   // 4.8.12.8 - Step 3:
   // Let promise be a new promise and append promise to the list of pending
   // play promises.
-  RefPtr<Promise> promise = CreateDOMPromise(aRv);
-  if (NS_WARN_IF(aRv.Failed())) {
-    return nullptr;
-  }
   mPendingPlayPromises.AppendElement(promise);
 
   if (mPreloadAction == HTMLMediaElement::PRELOAD_NONE) {
     // The media load algorithm will be initiated by a user interaction.
     // We want to boost the channel priority for better responsiveness.
     // Note this must be done before UpdatePreloadAction() which will
     // update |mPreloadAction|.
     mUseUrgentStartForChannel = true;
@@ -4071,18 +4078,18 @@ HTMLMediaElement::PlayInternal(ErrorResu
           // If something wrong between |mPendingPlayPromises.AppendElement(promise);|
           // and here, the _promise_ should already have been rejected. Otherwise,
           // the _promise_ won't be returned to JS at all, so just leave it in the
           // _mPendingPlayPromises_ and let it be resolved/rejected with the
           // following actions and the promise-resolution won't be observed at all.
           LOG(LogLevel::Debug,
               ("%p Play() promise rejected because failed to play MediaDecoder.",
               this));
-          aRv.Throw(rv);
-          return nullptr;
+          promise->MaybeReject(rv);
+          return promise.forget();
         }
       }
     }
   } else if (mReadyState < HAVE_METADATA) {
     mAttemptPlayUponLoadedMetadata = true;
   }
 
   if (mCurrentPlayRangeStart == -1.0) {
@@ -7588,30 +7595,46 @@ HTMLMediaElement::UpdateCustomPolicyAfte
 AbstractThread*
 HTMLMediaElement::AbstractMainThread() const
 {
   MOZ_ASSERT(mAbstractMainThread);
 
   return mAbstractMainThread;
 }
 
-nsTArray<RefPtr<Promise>>
+nsTArray<RefPtr<PlayPromise>>
 HTMLMediaElement::TakePendingPlayPromises()
 {
   return Move(mPendingPlayPromises);
 }
 
 void
 HTMLMediaElement::NotifyAboutPlaying()
 {
   // Stick to the DispatchAsyncEvent() call path for now because we want to
   // trigger some telemetry-related codes in the DispatchAsyncEvent() method.
   DispatchAsyncEvent(NS_LITERAL_STRING("playing"));
 }
 
+already_AddRefed<PlayPromise>
+HTMLMediaElement::CreatePlayPromise(ErrorResult& aRv) const
+{
+  nsPIDOMWindowInner* win = OwnerDoc()->GetInnerWindow();
+
+  if (!win) {
+    aRv.Throw(NS_ERROR_UNEXPECTED);
+    return nullptr;
+  }
+
+  RefPtr<PlayPromise> promise = PlayPromise::Create(win->AsGlobal(), aRv);
+  LOG(LogLevel::Debug, ("%p created PlayPromise %p", this, promise.get()));
+
+  return promise.forget();
+}
+
 already_AddRefed<Promise>
 HTMLMediaElement::CreateDOMPromise(ErrorResult& aRv) const
 {
   nsPIDOMWindowInner* win = OwnerDoc()->GetInnerWindow();
 
   if (!win) {
     aRv.Throw(NS_ERROR_UNEXPECTED);
     return nullptr;

--- a/dom/html/HTMLMediaElement.h
+++ b/dom/html/HTMLMediaElement.h
@@ -77,16 +77,17 @@ class nsRange;
 namespace mozilla {
 namespace dom {
 
 // Number of milliseconds between timeupdate events as defined by spec
 #define TIMEUPDATE_MS 250
 
 class MediaError;
 class MediaSource;
+class PlayPromise;
 class Promise;
 class TextTrackList;
 class AudioTrackList;
 class VideoTrackList;
 
 enum class StreamCaptureType : uint8_t
 {
   CAPTURE_ALL_TRACKS,
@@ -1321,17 +1322,17 @@ protected:
   nsresult DispatchEvent(const nsAString& aName);
 
   // Open unsupported types media with the external app when the media element
   // triggers play() after loaded fail. eg. preload the data before start play.
   void OpenUnsupportedMediaWithExternalAppIfNeeded() const;
 
   // This method moves the mPendingPlayPromises into a temperate object. So the
   // mPendingPlayPromises is cleared after this method call.
-  nsTArray<RefPtr<Promise>> TakePendingPlayPromises();
+  nsTArray<RefPtr<PlayPromise>> TakePendingPlayPromises();
 
   // This method snapshots the mPendingPlayPromises by TakePendingPlayPromises()
   // and queues a task to resolve them.
   void AsyncResolvePendingPlayPromises();
 
   // This method snapshots the mPendingPlayPromises by TakePendingPlayPromises()
   // and queues a task to reject them.
   void AsyncRejectPendingPlayPromises(nsresult aError);
@@ -1775,16 +1776,19 @@ public:
       return mCount + 1;
     }
   private:
     TimeStamp mStartTime;
     TimeDuration mSum;
     uint32_t mCount;
   };
 private:
+
+  already_AddRefed<PlayPromise> CreatePlayPromise(ErrorResult& aRv) const;
+
   /**
    * This function is called by AfterSetAttr and OnAttrSetButNotChanged.
    * It will not be called if the value is being unset.
    *
    * @param aNamespaceID the namespace of the attr being set
    * @param aName the localname of the attribute being set
    * @param aNotify Whether we plan to notify document observers.
    */
@@ -1836,17 +1840,17 @@ private:
 
   // This wrapper will handle all audio channel related stuffs, eg. the operations
   // of tab audio indicator, Fennec's media control.
   // Note: mAudioChannelWrapper might be null after GC happened.
   RefPtr<AudioChannelAgentCallback> mAudioChannelWrapper;
 
   // A list of pending play promises. The elements are pushed during the play()
   // method call and are resolved/rejected during further playback steps.
-  nsTArray<RefPtr<Promise>> mPendingPlayPromises;
+  nsTArray<RefPtr<PlayPromise>> mPendingPlayPromises;
 
   // A list of already-dispatched but not yet run
   // nsResolveOrRejectPendingPlayPromisesRunners.
   // Runners whose Run() method is called remove themselves from this list.
   // We keep track of these because the load algorithm resolves/rejects all
   // already-dispatched pending play promises.
   nsTArray<nsResolveOrRejectPendingPlayPromisesRunner*> mPendingPlayPromisesRunners;
 

new file mode 100644
--- /dev/null
+++ b/dom/html/PlayPromise.cpp
@@ -0,0 +1,126 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "mozilla/dom/PlayPromise.h"
+#include "mozilla/Logging.h"
+#include "mozilla/Telemetry.h"
+
+extern mozilla::LazyLogModule gMediaElementLog;
+
+#define PLAY_PROMISE_LOG(msg, ...)                                             \
+  MOZ_LOG(gMediaElementLog, LogLevel::Debug, (msg, ##__VA_ARGS__))
+
+namespace mozilla {
+namespace dom {
+
+PlayPromise::PlayPromise(nsIGlobalObject* aGlobal)
+  : Promise(aGlobal)
+{
+}
+
+PlayPromise::~PlayPromise()
+{
+  if (!mFulfilled && PromiseObj()) {
+    MaybeReject(NS_ERROR_DOM_ABORT_ERR);
+  }
+}
+
+/* static */
+already_AddRefed<PlayPromise>
+PlayPromise::Create(nsIGlobalObject* aGlobal, ErrorResult& aRv)
+{
+  RefPtr<PlayPromise> promise = new PlayPromise(aGlobal);
+  promise->CreateWrapper(nullptr, aRv);
+  return aRv.Failed() ? nullptr : promise.forget();
+}
+
+void
+PlayPromise::MaybeResolveWithUndefined()
+{
+  if (mFulfilled) {
+    return;
+  }
+  mFulfilled = true;
+  PLAY_PROMISE_LOG("PlayPromise %p resolved with undefined", this);
+  auto reason = Telemetry::LABELS_MEDIA_PLAY_PROMISE_RESOLUTION::Resolved;
+  Telemetry::AccumulateCategorical(reason);
+  Promise::MaybeResolveWithUndefined();
+}
+
+using PlayLabel = Telemetry::LABELS_MEDIA_PLAY_PROMISE_RESOLUTION;
+
+struct PlayPromiseTelemetryResult
+{
+  nsresult mValue;
+  PlayLabel mLabel;
+  const char* mName;
+};
+
+static const PlayPromiseTelemetryResult sPlayPromiseTelemetryResults[] = {
+  {
+    NS_ERROR_DOM_MEDIA_NOT_ALLOWED_ERR,
+    PlayLabel::NotAllowedErr,
+    "NotAllowedErr",
+  },
+  {
+    NS_ERROR_DOM_MEDIA_NOT_SUPPORTED_ERR,
+    PlayLabel::SrcNotSupportedErr,
+    "SrcNotSupportedErr",
+  },
+  {
+    NS_ERROR_DOM_MEDIA_ABORT_ERR,
+    PlayLabel::PauseAbortErr,
+    "PauseAbortErr",
+  },
+  {
+    NS_ERROR_DOM_ABORT_ERR,
+    PlayLabel::AbortErr,
+    "AbortErr",
+  },
+};
+
+static const PlayPromiseTelemetryResult*
+FindPlayPromiseTelemetryResult(nsresult aReason)
+{
+  for (const auto& p : sPlayPromiseTelemetryResults) {
+    if (p.mValue == aReason) {
+      return &p;
+    }
+  }
+  return nullptr;
+}
+
+static PlayLabel
+ToPlayResultLabel(nsresult aReason)
+{
+  auto p = FindPlayPromiseTelemetryResult(aReason);
+  return p ? p->mLabel : PlayLabel::UnknownErr;
+}
+
+static const char*
+ToPlayResultStr(nsresult aReason)
+{
+  auto p = FindPlayPromiseTelemetryResult(aReason);
+  return p ? p->mName : "UnknownErr";
+}
+
+void
+PlayPromise::MaybeReject(nsresult aReason)
+{
+  if (mFulfilled) {
+    return;
+  }
+  mFulfilled = true;
+  PLAY_PROMISE_LOG("PlayPromise %p rejected with 0x%x (%s)",
+                   this,
+                   static_cast<uint32_t>(aReason),
+                   ToPlayResultStr(aReason));
+  Telemetry::AccumulateCategorical(ToPlayResultLabel(aReason));
+  Promise::MaybeReject(aReason);
+}
+
+} // namespace dom
+} // namespace mozilla

new file mode 100644
--- /dev/null
+++ b/dom/html/PlayPromise.h
@@ -0,0 +1,35 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=2 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef __PlayPromise_h__
+#define __PlayPromise_h__
+
+#include "mozilla/dom/Promise.h"
+#include "mozilla/Telemetry.h"
+
+namespace mozilla {
+namespace dom {
+
+// Decorates a DOM Promise to report telemetry as to whether it was resolved
+// or rejected and why.
+class PlayPromise : public Promise
+{
+public:
+  static already_AddRefed<PlayPromise> Create(nsIGlobalObject* aGlobal,
+                                              ErrorResult& aRv);
+  ~PlayPromise();
+  void MaybeResolveWithUndefined();
+  void MaybeReject(nsresult aReason);
+
+private:
+  explicit PlayPromise(nsIGlobalObject* aGlobal);
+  bool mFulfilled = false;
+};
+
+} // namespace dom
+} // namespace mozilla
+
+#endif // __PlayPromise_h__

--- a/dom/html/moz.build
+++ b/dom/html/moz.build
@@ -117,16 +117,17 @@ EXPORTS.mozilla.dom += [
     'HTMLTimeElement.h',
     'HTMLTitleElement.h',
     'HTMLTrackElement.h',
     'HTMLUnknownElement.h',
     'HTMLVideoElement.h',
     'ImageDocument.h',
     'MediaError.h',
     'nsBrowserElement.h',
+    'PlayPromise.h',
     'RadioNodeList.h',
     'TextTrackManager.h',
     'TimeRanges.h',
     'ValidityState.h',
 ]
 
 UNIFIED_SOURCES += [
     'HTMLAllCollection.cpp',
@@ -206,16 +207,17 @@ UNIFIED_SOURCES += [
     'nsGenericHTMLElement.cpp',
     'nsGenericHTMLFrameElement.cpp',
     'nsHTMLContentSink.cpp',
     'nsHTMLDNSPrefetch.cpp',
     'nsHTMLDocument.cpp',
     'nsIConstraintValidation.cpp',
     'nsRadioVisitor.cpp',
     'nsTextEditorState.cpp',
+    'PlayPromise.cpp',
     'RadioNodeList.cpp',
     'TextTrackManager.cpp',
     'TimeRanges.cpp',
     'ValidityState.cpp',
     'VideoDocument.cpp',
 ]
 
 SOURCES += [

--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -11312,16 +11312,25 @@
     "expires_in_version": "60",
     "bug_numbers": [1230265],
     "kind": "linear",
     "high": 1000,
     "n_buckets": 100,
     "description": "720p VP9 decode benchmark measurement in frames per second",
     "releaseChannelCollection": "opt-out"
   },
+  "MEDIA_PLAY_PROMISE_RESOLUTION": {
+    "record_in_processes": ["main", "content"],
+    "bug_numbers": [1453176],
+    "alert_emails": ["cpearce@mozilla.com", "drno@ohlmeier.org"],
+    "expires_in_version": "72",
+    "kind": "categorical",
+    "labels": ["Resolved", "NotAllowedErr", "SrcNotSupportedErr", "PauseAbortErr", "AbortErr", "UnknownErr"],
+    "description": "Records whether promise returned by HTMLMediaElement.play() successfully resolved, or the error code which it was rejected with."
+  },
   "MEDIA_CODEC_USED": {
     "record_in_processes": ["main", "content"],
     "alert_emails": ["cpearce@mozilla.com"],
     "expires_in_version": "never",
     "keyed": true,
     "kind": "count",
     "description": "Count of use of audio/video codecs in HTMLMediaElements and WebAudio. Those with 'resource' prefix are approximate; report based on HTTP ContentType or sniffing. Those with 'webaudio' prefix are for WebAudio."
   },