diff --git a/dom/tests/mochitest/general/test_interfaces.html b/dom/tests/mochitest/general/test_interfaces.html
index 94509d340cc..86eb88bebad 100644
--- a/dom/tests/mochitest/general/test_interfaces.html
+++ b/dom/tests/mochitest/general/test_interfaces.html
@@ -293,6 +293,7 @@ var interfaceNamesInGlobalScope =
     "HTMLTextAreaElement",
     "HTMLTimeElement",
     "HTMLTitleElement",
+    {name: "HTMLTrackElement", release: false},
     "HTMLUListElement",
     "HTMLUnknownElement",
     "HTMLVideoElement",
@@ -565,6 +566,9 @@ var interfaceNamesInGlobalScope =
     "TextDecoder",
     "TextEncoder",
     "TextMetrics",
+    {name: "TextTrack", release: false},
+    {name: "TextTrackCueList", release: false},
+    {name: "TextTrackList", release: false},
     "TimeEvent",
     "TimeRanges",
     "Touch",
@@ -585,6 +589,9 @@ var interfaceNamesInGlobalScope =
     {name: "USSDReceivedEvent", b2g: true, pref: "dom.mobileconnection.enabled"},
     "ValidityState",
     "VideoStreamTrack",
+    {name: "VTTCue", release: false},
+    {name: "VTTRegion", release: false},
+    {name: "VTTRegionList", release: false},
     "WaveShaperNode",
     "WebGLActiveInfo",
     "WebGLBuffer",
diff --git a/modules/libpref/src/init/all.js b/modules/libpref/src/init/all.js
index 5d29f52f23e..c5c57600b25 100644
--- a/modules/libpref/src/init/all.js
+++ b/modules/libpref/src/init/all.js
@@ -263,7 +263,11 @@ pref("media.tabstreaming.height", 240);
 pref("media.tabstreaming.time_per_frame", 40);
 
 // TextTrack support
+#ifdef RELEASE_BUILD
 pref("media.webvtt.enabled", false);
+#else
+pref("media.webvtt.enabled", true);
+#endif
 
 // Whether to enable MediaSource support
 pref("media.mediasource.enabled", false);