--- a/dom/media/test/test_texttrackcue.html
+++ b/dom/media/test/test_texttrackcue.html
@@ -40,21 +40,23 @@ SpecialPowers.pushPrefEnv({"set": [["med
       is(trackElement.readyState, 2, "Track::ReadyState should be set to LOADED.");
       // Set mode to hidden so that the active cue lists are being updated.
       trackElement.track.mode = "hidden";
 
       var cueList = trackElement.track.cues;
       is(cueList.length, 6, "Cue list length should be 6.");
 
       // Check that the typedef of TextTrackCue works in Gecko.
-      is(window.TextTrackCue, undefined, "TextTrackCue should be undefined.");
+      isnot(window.TextTrackCue, undefined, "TextTrackCue should be defined.");
       isnot(window.VTTCue, undefined, "VTTCue should be defined.");
 
       // Check if first cue was parsed correctly.
       var cue = cueList[0];
+      ok(cue instanceof TextTrackCue, "Cue should be an instanceof TextTrackCue.");
+      ok(cue instanceof VTTCue, "Cue should be an instanceof VTTCue.");
       is(cue.id, "1", "Cue's ID should be 1.");
       is(cue.startTime, 0.5, "Cue's start time should be 0.5.");
       is(cue.endTime, 0.7, "Cue's end time should be 0.7.");
       is(cue.pauseOnExit, false, "Cue's pause on exit flag should be false.");
       is(cue.text, "This", "Cue's text should be set correctly.");
       is(cue.track, trackElement.track, "Cue's track should be defined.");
 
       cue.track = null;

--- a/dom/tests/mochitest/general/test_interfaces.html
+++ b/dom/tests/mochitest/general/test_interfaces.html
@@ -1271,16 +1271,18 @@ var interfaceNamesInGlobalScope =
     "TextDecoder",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "TextEncoder",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "TextMetrics",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "TextTrack",
 // IMPORTANT: Do not change this list without review from a DOM peer!
+    "TextTrackCue",
+// IMPORTANT: Do not change this list without review from a DOM peer!
     "TextTrackCueList",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "TextTrackList",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "TimeEvent",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "TimeRanges",
 // IMPORTANT: Do not change this list without review from a DOM peer!

new file mode 100644
--- /dev/null
+++ b/dom/webidl/TextTrackCue.webidl
@@ -0,0 +1,21 @@
+/* -*- 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://html.spec.whatwg.org/#texttrackcue
+ */
+
+[Pref="media.webvtt.enabled"]
+interface TextTrackCue : EventTarget {
+  readonly attribute TextTrack? track;
+
+  attribute DOMString id;
+  attribute double startTime;
+  attribute double endTime;
+  attribute boolean pauseOnExit;
+
+  attribute EventHandler onenter;
+  attribute EventHandler onexit;
+};
\ No newline at end of file

--- a/dom/webidl/VTTCue.webidl
+++ b/dom/webidl/VTTCue.webidl
@@ -1,15 +1,15 @@
 /* -*- 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
- * http://www.whatwg.org/specs/web-apps/current-work/#texttrackcue
+ * http://dev.w3.org/html5/webvtt/#the-vttcue-interface
  */
 
 enum AutoKeyword { "auto" };
 
 enum AlignSetting {
   "start",
   "middle",
   "end",
@@ -20,43 +20,33 @@ enum AlignSetting {
 enum DirectionSetting {
   "",
   "rl",
   "lr"
 };
 
 [Constructor(double startTime, double endTime, DOMString text),
  Pref="media.webvtt.enabled"]
-interface VTTCue : EventTarget {
-  readonly attribute TextTrack? track;
-
-  attribute DOMString id;
-  attribute double startTime;
-  attribute double endTime;
-  attribute boolean pauseOnExit;
+interface VTTCue : TextTrackCue {
   [Pref="media.webvtt.regions.enabled"]
   attribute VTTRegion? region;
   attribute DirectionSetting vertical;
   attribute boolean snapToLines;
   attribute (long or AutoKeyword) line;
   [SetterThrows]
   attribute AlignSetting lineAlign;
   [SetterThrows]
   attribute long position;
   [SetterThrows]
   attribute AlignSetting positionAlign;
   [SetterThrows]
   attribute long size;
   attribute AlignSetting align;
   attribute DOMString text;
   DocumentFragment getCueAsHTML();
-
-  attribute EventHandler onenter;
-
-  attribute EventHandler onexit;
 };
 
 // Mozilla extensions.
 partial interface VTTCue {
   [ChromeOnly]
   attribute HTMLDivElement? displayState;
   [ChromeOnly]
   readonly attribute boolean hasBeenReset;

--- a/dom/webidl/moz.build
+++ b/dom/webidl/moz.build
@@ -516,16 +516,17 @@ WEBIDL_FILES = [
     'Telephony.webidl',
     'TelephonyCall.webidl',
     'TelephonyCallGroup.webidl',
     'TelephonyCallId.webidl',
     'Text.webidl',
     'TextDecoder.webidl',
     'TextEncoder.webidl',
     'TextTrack.webidl',
+    'TextTrackCue.webidl',
     'TextTrackCueList.webidl',
     'TextTrackList.webidl',
     'ThreadSafeChromeUtils.webidl',
     'TimeEvent.webidl',
     'TimeRanges.webidl',
     'Touch.webidl',
     'TouchEvent.webidl',
     'TouchList.webidl',

--- a/testing/web-platform/meta/html/dom/interfaces.html.ini
+++ b/testing/web-platform/meta/html/dom/interfaces.html.ini
@@ -1268,49 +1268,16 @@
     expected: FAIL
 
   [TextTrack interface: attribute oncuechange]
     expected: FAIL
 
   [TextTrack interface: document.createElement("track").track must inherit property "oncuechange" with the proper type (10)]
     expected: FAIL
 
-  [TextTrackCue interface: existence and properties of interface object]
-    expected: FAIL
-
-  [TextTrackCue interface object length]
-    expected: FAIL
-
-  [TextTrackCue interface: existence and properties of interface prototype object]
-    expected: FAIL
-
-  [TextTrackCue interface: existence and properties of interface prototype object's "constructor" property]
-    expected: FAIL
-
-  [TextTrackCue interface: attribute track]
-    expected: FAIL
-
-  [TextTrackCue interface: attribute id]
-    expected: FAIL
-
-  [TextTrackCue interface: attribute startTime]
-    expected: FAIL
-
-  [TextTrackCue interface: attribute endTime]
-    expected: FAIL
-
-  [TextTrackCue interface: attribute pauseOnExit]
-    expected: FAIL
-
-  [TextTrackCue interface: attribute onenter]
-    expected: FAIL
-
-  [TextTrackCue interface: attribute onexit]
-    expected: FAIL
-
   [TrackEvent must be primary interface of new TrackEvent("addtrack"; {track:document.createElement("track").track})]
     expected: FAIL
 
   [Stringification of new TrackEvent("addtrack"; {track:document.createElement("track").track})]
     expected: FAIL
 
   [TrackEvent interface: new TrackEvent("addtrack"; {track:document.createElement("track").track}) must inherit property "track" with the proper type (0)]
     expected: FAIL

--- a/testing/web-platform/meta/html/semantics/embedded-content/media-elements/historical.html.ini
+++ b/testing/web-platform/meta/html/semantics/embedded-content/media-elements/historical.html.ini
@@ -1,8 +1,5 @@
 [historical.html]
   type: testharness
   [source.media should not be supported]
     expected: FAIL
 
-  [TextTrackCue constructor should not be supported]
-    expected: FAIL
-