--- a/dom/media/tests/mochitest/identity/test_fingerprints.html
+++ b/dom/media/tests/mochitest/identity/test_fingerprints.html
@@ -56,19 +56,19 @@ function testMultipleFingerprints() {
   var pcDouble = new RTCPeerConnection({});
 
   var offer, match, fingerprints;
 
   var fail = msg =>
       (e => ok(false, 'error in ' + msg + ': ' +
                (e.message ? (e.message + '\n' + e.stack) : e)));
 
-  navigator.mediaDevices.getUserMedia({ audio: true, fake: true })
+  navigator.mediaDevices.getUserMedia({ audio: true })
     .then(stream => {
-      ok(stream, 'Got fake stream');
+      ok(stream, 'Got test stream');
       pcDouble.addStream(stream);
       return pcDouble.createOffer();
     })
     .then(o => {
       offer = o;
       ok(offer, 'Got offer');
 
       match = offer.sdp.match(fingerprintRegex);
@@ -99,13 +99,23 @@ function testMultipleFingerprints() {
       pcStrict.close();
       pcDouble.close();
       SimpleTest.finish();
     });
 }
 
 SimpleTest.waitForExplicitFinish();
 SpecialPowers.pushPrefEnv({
-  set: [ [ 'media.peerconnection.identity.enabled', true ] ]
+  set: [
+    [ 'media.peerconnection.identity.enabled', true ],
+    // Disable permission to skip prompt when on platforms the use loopback
+    // test devices (these would normally trigger a prompt).
+    [ 'media.navigator.permission.disabled', true ],
+    // Since this test doesn't include head.js or pc.js, we need to set the fake
+    // device pref manually. On platforms where loopback devices are used they
+    // should still take precedence, however on some platforms no prefs would
+    // be set and the test would fail.
+    [ 'media.navigator.streams.fake', true ]
+  ]
 }, testMultipleFingerprints);
 </script>
   </body>
 </html>

--- a/dom/media/tests/mochitest/test_getUserMedia_constraints.html
+++ b/dom/media/tests/mochitest/test_getUserMedia_constraints.html
@@ -43,20 +43,20 @@ var tests = [
   { message: "unknown mediaSource in audio fails",
     constraints: { audio: { mediaSource: 'uncle' } },
     error: "OverconstrainedError",
     constraint: "mediaSource" },
   { message: "emtpy constraint fails",
     constraints: { },
     error: "TypeError" },
   { message: "Triggering mock failure in default video device fails",
-    constraints: { video: { deviceId: 'bad device' }, fake: true },
+    constraints: { video: { deviceId: 'bad device' } },
     error: "NotReadableError" },
   { message: "Triggering mock failure in default audio device fails",
-    constraints: { audio: { deviceId: 'bad device' }, fake: true },
+    constraints: { audio: { deviceId: 'bad device' } },
     error: "NotReadableError" },
   { message: "Success-path: optional video facingMode + audio ignoring facingMode",
     constraints: { audio: { mediaSource: 'microphone',
                             facingMode: 'left',
                             foo: 0,
                             advanced: [{ facingMode: 'environment' },
                                        { facingMode: 'user' },
                                        { bar: 0 }] },
@@ -96,17 +96,23 @@ var mustFailWith = (msg, reason, constra
     }
   });
 
 /**
  * Starts the test run by running through each constraint
  * test by verifying that the right resolution and rejection is fired.
  */
 
-runTest(() => Promise.resolve()
+runTest(() => pushPrefs(
+    // This test expects fake devices, particularly for the 'triggering mock
+    // failure *' steps. So explicitly disable loopback and setup fakes
+    ['media.audio_loopback_dev', ''],
+    ['media.video_loopback_dev', ''],
+    ['media.navigator.streams.fake', true]
+  )
   .then(() => {
     // Check supported constraints first.
     var dict = navigator.mediaDevices.getSupportedConstraints();
     var supported = Object.keys(dict);
 
     mustSupport.forEach(key => ok(supported.includes(key) && dict[key],
                                   "Supports " + key));
 

--- a/dom/media/tests/mochitest/test_getUserMedia_mediaElementCapture_video.html
+++ b/dom/media/tests/mochitest/test_getUserMedia_mediaElementCapture_video.html
@@ -15,18 +15,25 @@ createHTML({
 });
 
 var gUMVideoElement;
 var captureStreamElement;
 
 const pausedTimeout = 1000;
 let h;
 
-runTest(() => getUserMedia({video: true, fake: true})
-  .then(stream => {
+runTest(async () => {
+  try {
+    await pushPrefs(
+      // This test expects fake video devices, as it expects captured frames to
+      // shift over time, which is not currently provided by loopback devices
+      ['media.video_loopback_dev', ''],
+      ['media.navigator.streams.fake', true]);
+
+    let stream = await getUserMedia({video: true});
     h = new VideoStreamHelper();
     gUMVideoElement =
       createMediaElement("video", "gUMVideo");
     gUMVideoElement.srcObject = stream;
     gUMVideoElement.play();
 
     info("Capturing");
     captureStreamElement =
@@ -37,58 +44,47 @@ runTest(() => getUserMedia({video: true,
     // Adding a dummy audio track to the stream will keep a consuming media
     // element from ending.
     // We could also solve it by repeatedly play()ing or autoplay, but then we
     // wouldn't be sure the media element stopped rendering video because it
     // went to the ended state or because there were no frames for the track.
     let osc = createOscillatorStream(new AudioContext(), 1000);
     captureStreamElement.srcObject.addTrack(osc.getTracks()[0]);
 
-    return h.checkVideoPlaying(captureStreamElement);
-  })
-  .then(() => {
+    await h.checkVideoPlaying(captureStreamElement);
     info("Video flowing. Pausing.");
     gUMVideoElement.pause();
+    await h.checkVideoPaused(captureStreamElement, { time: pausedTimeout });
 
-    return h.checkVideoPaused(captureStreamElement, { time: pausedTimeout });
-  })
-  .then(() => {
     info("Video stopped flowing. Playing.");
     gUMVideoElement.play();
+    await h.checkVideoPlaying(captureStreamElement);
 
-    return h.checkVideoPlaying(captureStreamElement);
-  })
-  .then(() => {
     info("Video flowing. Removing source.");
-    var stream = gUMVideoElement.srcObject;
+    stream = gUMVideoElement.srcObject;
     gUMVideoElement.srcObject = null;
+    await h.checkVideoPaused(captureStreamElement, { time: pausedTimeout });
 
-    return h.checkVideoPaused(captureStreamElement, { time: pausedTimeout })
-        .then(() => stream);
-  })
-  .then(stream => {
     info("Video stopped flowing. Setting source.");
     gUMVideoElement.srcObject = stream;
-    return h.checkVideoPlaying(captureStreamElement);
-  })
-  .then(() => {
+    await h.checkVideoPlaying(captureStreamElement);
+
     info("Video flowing. Changing source by track manipulation. Remove first.");
-    var track = gUMVideoElement.srcObject.getTracks()[0];
+    let track = gUMVideoElement.srcObject.getTracks()[0];
     gUMVideoElement.srcObject.removeTrack(track);
-    return h.checkVideoPaused(captureStreamElement, { time: pausedTimeout })
-        .then(() => track);
-  })
-  .then(track => {
+    await h.checkVideoPaused(captureStreamElement, { time: pausedTimeout });
+
     info("Video paused. Changing source by track manipulation. Add first.");
     gUMVideoElement.srcObject.addTrack(track);
     gUMVideoElement.play();
-    return h.checkVideoPlaying(captureStreamElement);
-  })
-  .then(() => {
+    await h.checkVideoPlaying(captureStreamElement);
+
     gUMVideoElement.srcObject.getTracks().forEach(t => t.stop());
     ok(true, "Test passed.");
-  })
-  .catch(e => ok(false, "Test failed: " + e + (e.stack ? "\n" + e.stack : ""))));
+  } catch (e) {
+    ok(false, "Test failed: " + e + (e.stack ? "\n" + e.stack : ""));
+  }
+});
 
 </script>
 </pre>
 </body>
 </html>

--- a/dom/media/tests/mochitest/test_peerConnection_addSecondVideoStream.html
+++ b/dom/media/tests/mochitest/test_peerConnection_addSecondVideoStream.html
@@ -7,26 +7,30 @@
 <body>
 <pre id="test">
 <script type="application/javascript">
   createHTML({
     bug: "1017888",
     title: "Renegotiation: add second video stream"
   });
 
-  runNetworkTest(function (options) {
+  runNetworkTest(async function (options) {
+    // Use fake video here since the native fake device on linux doesn't
+    // change color as needed by checkVideoPlaying() below.
+    await pushPrefs(
+      ['media.video_loopback_dev', ''],
+      ['media.navigator.streams.fake', true]);
+
     const test = new PeerConnectionTest(options);
     addRenegotiation(test.chain,
       [
         function PC_LOCAL_ADD_SECOND_STREAM(test) {
           test.setMediaConstraints([{video: true}, {video: true}],
                                    [{video: true}]);
-          // Use fake:true here since the native fake device on linux doesn't
-          // change color as needed by checkVideoPlaying() below.
-          return test.pcLocal.getAllUserMediaAndAddStreams([{video: true, fake: true}]);
+          return test.pcLocal.getAllUserMediaAndAddStreams([{video: true}]);
         },
       ],
       [
         function PC_REMOTE_CHECK_VIDEO_FLOW(test) {
           const h = new VideoStreamHelper();
           is(test.pcRemote.remoteMediaElements.length, 2,
              "Should have two remote media elements after renegotiation");
           return Promise.all(test.pcRemote.remoteMediaElements.map(video =>

--- a/dom/media/tests/mochitest/test_peerConnection_addSecondVideoStreamNoBundle.html
+++ b/dom/media/tests/mochitest/test_peerConnection_addSecondVideoStreamNoBundle.html
@@ -7,45 +7,49 @@
 <body>
 <pre id="test">
 <script type="application/javascript">
   createHTML({
     bug: "1017888",
     title: "Renegotiation: add second video stream, no bundle"
   });
 
-  runNetworkTest(function (options = {}) {
+  runNetworkTest(async function (options = {}) {
+    // Use fake video here since the native fake device on linux doesn't
+    // change color as needed by checkVideoPlaying() below.
+    await pushPrefs(
+      ['media.video_loopback_dev', ''],
+      ['media.navigator.streams.fake', true]);
+
     options.bundle = false;
     const test = new PeerConnectionTest(options);
     addRenegotiation(test.chain,
       [
         function PC_LOCAL_ADD_SECOND_STREAM(test) {
           test.setMediaConstraints([{video: true}, {video: true}],
                                    [{video: true}]);
           // Since this is a NoBundle variant, adding a track will cause us to
           // go back to checking.
           test.pcLocal.expectIceChecking();
-          // Use fake:true here since the native fake device on linux doesn't
-          // change color as needed by checkVideoPlaying() below.
-          return test.pcLocal.getAllUserMediaAndAddStreams([{video: true, fake: true}]);
+          return test.pcLocal.getAllUserMediaAndAddStreams([{video: true}]);
         },
         function PC_REMOTE_EXPECT_ICE_CHECKING(test) {
           test.pcRemote.expectIceChecking();
         },
       ],
       [
         function PC_REMOTE_CHECK_VIDEO_FLOW(test) {
           const h = new VideoStreamHelper();
           is(test.pcRemote.remoteMediaElements.length, 2,
              "Should have two remote media elements after renegotiation");
           return Promise.all(test.pcRemote.remoteMediaElements.map(video =>
             h.checkVideoPlaying(video)));
         },
       ]
     );
 
-    test.setMediaConstraints([{video: true, fake: true}], [{video: true}]);
+    test.setMediaConstraints([{video: true}], [{video: true}]);
     test.run();
   });
 </script>
 </pre>
 </body>
 </html>

--- a/dom/media/tests/mochitest/test_peerConnection_audioCodecs.html
+++ b/dom/media/tests/mochitest/test_peerConnection_audioCodecs.html
@@ -15,17 +15,17 @@
   // So all other present codecs can be removed.
   const codecs = [ "opus", "G722", "PCMU", "PCMA" ];
 
   async function testAudioCodec(options = {}, codec) {
     // sdputils checks for opus as part of its sdp sanity test
     options.opus = codec == "opus";
 
     let test = new PeerConnectionTest(options);
-    test.setMediaConstraints([{audio: true, fake: true}], []);
+    test.setMediaConstraints([{audio: true}], []);
 
     test.chain.insertBefore("PC_LOCAL_SET_LOCAL_DESCRIPTION", [
       function PC_LOCAL_FILTER_OUT_CODECS() {
         let otherCodec = codecs.find(c => c != codec);
         let otherId = sdputils.findCodecId(test.originalOffer.sdp, otherCodec);
 
         let id = sdputils.findCodecId(test.originalOffer.sdp, codec);
         test.originalOffer.sdp =

--- a/dom/media/tests/mochitest/test_peerConnection_removeThenAddVideoTrack.html
+++ b/dom/media/tests/mochitest/test_peerConnection_removeThenAddVideoTrack.html
@@ -7,17 +7,23 @@
 <body>
 <pre id="test">
 <script type="application/javascript">
   createHTML({
     bug: "1017888",
     title: "Renegotiation: remove then add video track"
   });
 
-  runNetworkTest(function (options) {
+  runNetworkTest(async function (options) {
+    // Use fake video here since the native fake device on linux doesn't
+    // change color as needed by checkVideoPlaying() below.
+    await pushPrefs(
+      ['media.video_loopback_dev', ''],
+      ['media.navigator.streams.fake', true]);
+
     const test = new PeerConnectionTest(options);
     const helper = new VideoStreamHelper();
     var originalTrack;
     let haveMuteEvent = new Promise(() => {});
     let haveUnmuteEvent = new Promise(() => {});
     addRenegotiation(test.chain,
       [
         function PC_REMOTE_FIND_RECEIVER(test) {
@@ -28,19 +34,17 @@
         function PC_LOCAL_REMOVE_VIDEO_TRACK(test) {
           // The new track's pipeline will start with a packet count of
           // 0, but the remote side will keep its old pipeline and packet
           // count.
           test.pcLocal.disableRtpCountChecking = true;
           return test.pcLocal.removeSender(0);
         },
         function PC_LOCAL_ADD_VIDEO_TRACK(test) {
-          // Use fake:true here since the native fake device on linux doesn't
-          // change color as needed by checkVideoPlaying() below.
-          return test.pcLocal.getAllUserMediaAndAddStreams([{video: true, fake: true}]);
+          return test.pcLocal.getAllUserMediaAndAddStreams([{video: true}]);
         },
       ],
       [
         function PC_REMOTE_WAIT_FOR_UNMUTE() {
           return haveUnmuteEvent;
         },
         function PC_REMOTE_CHECK_ADDED_TRACK(test) {
           is(test.pcRemote._pc.getTransceivers().length, 2,

--- a/dom/media/tests/mochitest/test_peerConnection_removeThenAddVideoTrackNoBundle.html
+++ b/dom/media/tests/mochitest/test_peerConnection_removeThenAddVideoTrackNoBundle.html
@@ -7,17 +7,23 @@
 <body>
 <pre id="test">
 <script type="application/javascript">
   createHTML({
     bug: "1017888",
     title: "Renegotiation: remove then add video track, no bundle"
   });
 
-  runNetworkTest(function (options) {
+  runNetworkTest(async function (options) {
+    // Use fake video here since the native fake device on linux doesn't
+    // change color as needed by checkVideoPlaying() below.
+    await pushPrefs(
+      ['media.video_loopback_dev', ''],
+      ['media.navigator.streams.fake', true]);
+
     options = options || { };
     options.bundle = false;
     const test = new PeerConnectionTest(options);
     const helper = new VideoStreamHelper();
     var originalTrack;
     addRenegotiation(test.chain,
       [
         function PC_REMOTE_FIND_RECEIVER(test) {
@@ -30,17 +36,17 @@
           // 0, but the remote side will keep its old pipeline and packet
           // count.
           test.pcLocal.disableRtpCountChecking = true;
           return test.pcLocal.removeSender(0);
         },
         function PC_LOCAL_ADD_VIDEO_TRACK(test) {
           // Use fake:true here since the native fake device on linux doesn't
           // change color as needed by checkVideoPlaying() below.
-          return test.pcLocal.getAllUserMediaAndAddStreams([{video: true, fake: true}]);
+          return test.pcLocal.getAllUserMediaAndAddStreams([{video: true}]);
         },
         function PC_LOCAL_EXPECT_ICE_CHECKING(test) {
           test.pcLocal.expectIceChecking();
         },
         function PC_REMOTE_EXPECT_ICE_CHECKING(test) {
           test.pcRemote.expectIceChecking();
         },
       ],

--- a/dom/media/tests/mochitest/test_peerConnection_trackDisabling.html
+++ b/dom/media/tests/mochitest/test_peerConnection_trackDisabling.html
@@ -14,17 +14,22 @@ createHTML({
 
 runNetworkTest(async () => {
   var test = new PeerConnectionTest();
 
   await pushPrefs(
     ["media.getusermedia.camera.stop_on_disable.enabled", true],
     ["media.getusermedia.camera.stop_on_disable.delay_ms", 0],
     ["media.getusermedia.microphone.stop_on_disable.enabled", true],
-    ["media.getusermedia.microphone.stop_on_disable.delay_ms", 0]);
+    ["media.getusermedia.microphone.stop_on_disable.delay_ms", 0],
+    // Always use fake tracks since we depend on video to be somewhat green and
+    // audio to have a large 1000Hz component (or 440Hz if using fake devices).
+    ['media.audio_loopback_dev', ''],
+    ['media.video_loopback_dev', ''],
+    ['media.navigator.streams.fake', true]);
 
   test.setMediaConstraints([{audio: true, video: true}], []);
   test.chain.append([
     function CHECK_ASSUMPTIONS() {
       is(test.pcLocal.localMediaElements.length, 2,
          "pcLocal should have one media element");
       is(test.pcRemote.remoteMediaElements.length, 2,
          "pcRemote should have one media element");

--- a/dom/media/tests/mochitest/test_peerConnection_trackDisabling_clones.html
+++ b/dom/media/tests/mochitest/test_peerConnection_trackDisabling_clones.html
@@ -14,17 +14,21 @@ createHTML({
 
 runNetworkTest(async () => {
   var test = new PeerConnectionTest();
 
   await pushPrefs(
     ["media.getusermedia.camera.stop_on_disable.enabled", true],
     ["media.getusermedia.camera.stop_on_disable.delay_ms", 0],
     ["media.getusermedia.microphone.stop_on_disable.enabled", true],
-    ["media.getusermedia.microphone.stop_on_disable.delay_ms", 0]);
+    ["media.getusermedia.microphone.stop_on_disable.delay_ms", 0],
+    // Always use fake tracks since we depend on audio to have a large 1000Hz
+    // component.
+    ['media.audio_loopback_dev', ''],
+    ['media.navigator.streams.fake', true]);
 
   var originalStream;
   var localVideoOriginal;
 
   test.setMediaConstraints([{audio: true, video: true}], []);
   test.chain.replace("PC_LOCAL_GUM", [
     function PC_LOCAL_GUM_CLONE() {
       return getUserMedia(test.pcLocal.constraints[0]).then(stream => {

--- a/dom/media/tests/mochitest/test_peerConnection_videoCodecs.html
+++ b/dom/media/tests/mochitest/test_peerConnection_videoCodecs.html
@@ -9,17 +9,17 @@
 <script type="application/javascript">
   createHTML({
     bug: "1395853",
     title: "Verify video content over WebRTC for every video codec",
   });
 
   async function testVideoCodec(options = {}, codec) {
     let test = new PeerConnectionTest(options);
-    test.setMediaConstraints([{video: true, fake: true}], []);
+    test.setMediaConstraints([{video: true}], []);
 
     test.chain.insertBefore("PC_LOCAL_SET_LOCAL_DESCRIPTION", [
       function PC_LOCAL_FILTER_OUT_CODECS() {
         let otherCodec = codecs.find(c => c != codec);
         let otherId = sdputils.findCodecId(test.originalOffer.sdp, otherCodec.name, otherCodec.offset);
         let otherRtpmapMatcher = new RegExp(`a=rtpmap:${otherId}.*\\r\\n`, "gi");
 
         let id = sdputils.findCodecId(test.originalOffer.sdp, codec.name, codec.offset);
@@ -67,16 +67,21 @@
   const codecs = [
     { name: "VP8" },
     { name: "VP9" },
     { name: "H264" },
     { name: "H264", offset: 1 },
   ];
 
   runNetworkTest(async (options) => {
+    // This test expects the video being captured will change color. Use fake
+    // video device as loopback does not currently change.
+    await pushPrefs(
+      ['media.video_loopback_dev', ''],
+      ['media.navigator.streams.fake', true]);
     for (let codec of codecs) {
       info(`Testing video for codec ${codec.name}`);
       try {
         await testVideoCodec(options, codec);
       } catch(e) {
         ok(false, `Error in test for codec ${codec.name}: ${e}\n${e.stack}`);
       }
       info(`Tested video for codec ${codec.name}`);

--- a/dom/media/webaudio/test/test_mediaStreamAudioSourceNodeNoGC.html
+++ b/dom/media/webaudio/test/test_mediaStreamAudioSourceNodeNoGC.html
@@ -45,45 +45,51 @@ function waitForAudio(analysisFunction, 
         return;
       }
       requestAnimationFrame(loop);
     };
     loop();
   });
 }
 
-navigator.mediaDevices.getUserMedia({audio: true, fake: true})
-  .then(stream => {
+SpecialPowers.pushPrefEnv({
+  set: [
+    // This test expects the fake audio device, specifically for the tones
+    // it outputs. Explicitly disable the audio loopback device and enable
+    // fake streams.
+    ['media.audio_loopback_dev', ''],
+    ['media.navigator.streams.fake', true]
+  ]
+}).then(async () => {
+  try {
+    let stream = await navigator.mediaDevices.getUserMedia({audio: true});
     stream.onended = () => ended = true;
     let source = context.createMediaStreamSource(stream);
     source.connect(analyser);
-    analyser.connect(context.destination);
-  })
-  .then(() => {
+    await analyser.connect(context.destination);
+
     ok(true, "Waiting for audio to pass through the analyser")
-    return waitForAudio(arr => arr[binIndexForFrequency(1000)] > 200,
-                        wait(60000, "Timeout waiting for audio"));
-  })
-  .then(() => {
+    await waitForAudio(arr => arr[binIndexForFrequency(1000)] > 200,
+                       wait(60000, "Timeout waiting for audio"));
+
     ok(true, "Audio was detected by the analyser. Forcing CC.");
     SpecialPowers.forceCC();
     SpecialPowers.forceGC();
     SpecialPowers.forceCC();
     SpecialPowers.forceGC();
 
     info("Checking that GC didn't destroy the stream or source node");
-    return waitForAudio(arr => arr[binIndexForFrequency(1000)] < 50,
-                        wait(5000, "Timeout waiting for GC (timeout OK)"))
+    await waitForAudio(arr => arr[binIndexForFrequency(1000)] < 50,
+                       wait(5000, "Timeout waiting for GC (timeout OK)"))
                   .then(() => Promise.reject("Audio stopped unexpectedly"),
                         () => Promise.resolve());
-  })
-  .then(() => {
+
     ok(true, "Audio is still flowing");
     SimpleTest.finish();
-  })
-  .catch(e => {
+  } catch(e) {
     ok(false, "Error executing test: " + e + (e.stack ? "\n" + e.stack : ""));
     SimpleTest.finish();
-  });
+  }
+});
 </script>
 </pre>
 </body>
 </html>