diff --git a/dom/media/webrtc/jsapi/RTCRtpReceiver.cpp b/dom/media/webrtc/jsapi/RTCRtpReceiver.cpp
index 972b81adba57..26ba57cb19f7 100644
--- a/dom/media/webrtc/jsapi/RTCRtpReceiver.cpp
+++ b/dom/media/webrtc/jsapi/RTCRtpReceiver.cpp
@@ -571,18 +571,6 @@ void RTCRtpReceiver::UpdateStreams(StreamAssociationChanges* aChanges) {
   }
 }
 
-void RTCRtpReceiver::MozAddRIDExtension(unsigned short aExtensionId) {
-  if (mPipeline) {
-    mPipeline->AddRIDExtension_m(aExtensionId);
-  }
-}
-
-void RTCRtpReceiver::MozAddRIDFilter(const nsAString& aRid) {
-  if (mPipeline) {
-    mPipeline->AddRIDFilter_m(NS_ConvertUTF16toUTF8(aRid).get());
-  }
-}
-
 // test-only: adds fake CSRCs and audio data
 void RTCRtpReceiver::MozInsertAudioLevelForContributingSource(
     const uint32_t aSource, const DOMHighResTimeStamp aTimestamp,
diff --git a/dom/media/webrtc/jsapi/RTCRtpReceiver.h b/dom/media/webrtc/jsapi/RTCRtpReceiver.h
index 61ebf3b8f299..ee370474eb49 100644
--- a/dom/media/webrtc/jsapi/RTCRtpReceiver.h
+++ b/dom/media/webrtc/jsapi/RTCRtpReceiver.h
@@ -60,9 +60,6 @@ class RTCRtpReceiver : public nsISupports,
       nsTArray<dom::RTCRtpContributingSource>& aSources);
   void GetSynchronizationSources(
       nsTArray<dom::RTCRtpSynchronizationSource>& aSources);
-  // test-only: called from simulcast mochitests.
-  void MozAddRIDExtension(unsigned short aExtensionId);
-  void MozAddRIDFilter(const nsAString& aRid);
   // test-only: insert fake CSRCs and audio levels for testing
   void MozInsertAudioLevelForContributingSource(
       const uint32_t aSource, const DOMHighResTimeStamp aTimestamp,
diff --git a/dom/media/webrtc/tests/mochitests/mochitest.ini b/dom/media/webrtc/tests/mochitests/mochitest.ini
index c71351d1b70e..ecd001f1bae3 100644
--- a/dom/media/webrtc/tests/mochitests/mochitest.ini
+++ b/dom/media/webrtc/tests/mochitests/mochitest.ini
@@ -20,6 +20,8 @@ support-files =
   parser_rtp.js
   peerconnection_audio_forced_sample_rate.js
   iceTestUtils.js
+  simulcast.js
+  helpers_from_wpt/sdp.js
   !/dom/canvas/test/captureStream_common.js
   !/dom/canvas/test/webgl-mochitest/webgl-util.js
   !/dom/media/test/manifest.js
diff --git a/dom/media/webrtc/tests/mochitests/simulcast.js b/dom/media/webrtc/tests/mochitests/simulcast.js
new file mode 100644
index 000000000000..127468b72686
--- /dev/null
+++ b/dom/media/webrtc/tests/mochitests/simulcast.js
@@ -0,0 +1,140 @@
+"use strict";
+/* Helper functions to munge SDP and split the sending track into
+ * separate tracks on the receiving end. This can be done in a number
+ * of ways, the one used here uses the fact that the MID and RID header
+ * extensions which are used for packet routing share the same wire
+ * format. The receiver interprets the rids from the sender as mids
+ * which allows receiving the different spatial resolutions on separate
+ * m-lines and tracks.
+ */
+
+// Adapted from wpt to improve handling of cases where answerer is the
+// simulcast sender, better handling of a=setup and direction attributes, and
+// some simplification. Will probably end up merging back at some point.
+
+const ridExtensions = [
+  "urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id",
+  "urn:ietf:params:rtp-hdrext:sdes:repaired-rtp-stream-id",
+];
+
+function ridToMid(sdpString) {
+  const sections = SDPUtils.splitSections(sdpString);
+  const dtls = SDPUtils.getDtlsParameters(sections[1], sections[0]);
+  const ice = SDPUtils.getIceParameters(sections[1], sections[0]);
+  const rtpParameters = SDPUtils.parseRtpParameters(sections[1]);
+  const setupValue = sdpString.match(/a=setup:(.*)/)[1];
+  const directionValue =
+    sdpString.match(/a=sendrecv|a=sendonly|a=recvonly|a=inactive/) ||
+    "a=sendrecv";
+
+  // Skip mid extension; we are replacing it with the rid extmap
+  rtpParameters.headerExtensions = rtpParameters.headerExtensions.filter(
+    ext => {
+      return ext.uri != "urn:ietf:params:rtp-hdrext:sdes:mid";
+    }
+  );
+
+  rtpParameters.headerExtensions.forEach(ext => {
+    if (ext.uri == "urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id") {
+      ext.uri = "urn:ietf:params:rtp-hdrext:sdes:mid";
+    }
+  });
+
+  let rids = Array.from(sdpString.matchAll(/a=rid:(.*) send/g)).map(r => r[1]);
+
+  let sdp =
+    SDPUtils.writeSessionBoilerplate() +
+    SDPUtils.writeDtlsParameters(dtls, setupValue) +
+    SDPUtils.writeIceParameters(ice) +
+    "a=group:BUNDLE " +
+    rids.join(" ") +
+    "\r\n";
+  const baseRtpDescription = SDPUtils.writeRtpDescription(
+    "video",
+    rtpParameters
+  );
+  rids.forEach(rid => {
+    sdp +=
+      baseRtpDescription +
+      "a=mid:" +
+      rid +
+      "\r\n" +
+      "a=msid:rid-" +
+      rid +
+      " rid-" +
+      rid +
+      "\r\n";
+    sdp += directionValue + "\r\n";
+  });
+
+  return sdp;
+}
+
+function midToRid(sdpString) {
+  const sections = SDPUtils.splitSections(sdpString);
+  const dtls = SDPUtils.getDtlsParameters(sections[1], sections[0]);
+  const ice = SDPUtils.getIceParameters(sections[1], sections[0]);
+  const rtpParameters = SDPUtils.parseRtpParameters(sections[1]);
+  const setupValue = sdpString.match(/a=setup:(.*)/)[1];
+  const directionValue =
+    sdpString.match(/a=sendrecv|a=sendonly|a=recvonly|a=inactive/) ||
+    "a=sendrecv";
+
+  // Skip rid extensions; we are replacing them with the mid extmap
+  rtpParameters.headerExtensions = rtpParameters.headerExtensions.filter(
+    ext => {
+      return !ridExtensions.includes(ext.uri);
+    }
+  );
+
+  rtpParameters.headerExtensions.forEach(ext => {
+    if (ext.uri == "urn:ietf:params:rtp-hdrext:sdes:mid") {
+      ext.uri = "urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id";
+    }
+  });
+
+  let mids = [];
+  for (let i = 1; i < sections.length; i++) {
+    mids.push(SDPUtils.getMid(sections[i]));
+  }
+
+  let sdp =
+    SDPUtils.writeSessionBoilerplate() +
+    SDPUtils.writeDtlsParameters(dtls, setupValue) +
+    SDPUtils.writeIceParameters(ice) +
+    "a=group:BUNDLE " +
+    mids[0] +
+    "\r\n";
+  sdp += SDPUtils.writeRtpDescription("video", rtpParameters);
+  // Although we are converting mids to rids, we still need a mid.
+  // The first one will be consistent with trickle ICE candidates.
+  sdp += "a=mid:" + mids[0] + "\r\n";
+  sdp += directionValue + "\r\n";
+
+  mids.forEach(mid => {
+    sdp += "a=rid:" + mid + " recv\r\n";
+  });
+  sdp += "a=simulcast:recv " + mids.join(";") + "\r\n";
+
+  return sdp;
+}
+
+// This would be useful for cases other than simulcast, but we do not use it
+// anywhere else right now, nor do we have a place for wpt-friendly helpers at
+// the moment.
+function createPlaybackElement(track) {
+  const elem = document.createElement(track.kind);
+  elem.autoplay = true;
+  elem.srcObject = new MediaStream([track]);
+  elem.id = track.id;
+  return elem;
+}
+
+async function getPlaybackWithLoadedMetadata(track) {
+  const elem = createPlaybackElement(track);
+  return new Promise(resolve => {
+    elem.addEventListener("loadedmetadata", () => {
+      resolve(elem);
+    });
+  });
+}
diff --git a/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastAnswer.html b/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastAnswer.html
index fdd490f4fdcf..254437cfc234 100644
--- a/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastAnswer.html
+++ b/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastAnswer.html
@@ -3,6 +3,8 @@
 <head>
   <script type="application/javascript" src="pc.js"></script>
   <script type="application/javascript" src="/tests/dom/canvas/test/captureStream_common.js"></script>
+  <script type="application/javascript" src="helpers_from_wpt/sdp.js"></script>
+  <script type="application/javascript" src="simulcast.js"></script>
 </head>
 <body>
 <pre id="test">
@@ -13,151 +15,90 @@
     visible: true
   });
 
-  function addRIDExtension(pc, extensionId) {
-    const receivers = pc._pc.getReceivers();
-    is(receivers.length, 1, "We have exactly one RTP receiver");
-    const receiver = receivers[0];
+  runNetworkTest(async () => {
+    await pushPrefs(
+        ['media.peerconnection.simulcast', true],
+        // 180Kbps was determined empirically, set well-higher than
+        // the 80Kbps+overhead needed for the two simulcast streams.
+        // 100Kbps was apparently too low.
+        ['media.peerconnection.video.min_bitrate_estimate', 180*1000]);
 
-    SpecialPowers.wrap(receiver).mozAddRIDExtension(extensionId);
-  }
 
-  function selectRecvRID(pc, rid) {
-    const receivers = pc._pc.getReceivers();
-    is(receivers.length, 1, "We have exactly one RTP receiver");
-    const receiver = receivers[0];
+    const offerer = new RTCPeerConnection();
+    const answerer = new RTCPeerConnection();
 
-    SpecialPowers.wrap(receiver).mozAddRIDFilter(rid);
-  }
+    const add = (pc, can, failed) => can && pc.addIceCandidate(can).catch(failed);
+    offerer.onicecandidate = e => add(answerer, e.candidate, generateErrorCallback());
+    answerer.onicecandidate = e => add(offerer, e.candidate, generateErrorCallback());
 
-  runNetworkTest(() =>
-    pushPrefs(['media.peerconnection.simulcast', true],
-              // 180Kbps was determined empirically, set well-higher than
-              // the 80Kbps+overhead needed for the two simulcast streams.
-              // 100Kbps was apparently too low.
-              ['media.peerconnection.video.min_bitrate_estimate', 180*1000]).then(() => {
-      let emitter, helper;
+    const metadataToBeLoaded = [];
+    offerer.ontrack = (e) => {
+      metadataToBeLoaded.push(getPlaybackWithLoadedMetadata(e.track));
+    };
 
-      test = new PeerConnectionTest({bundle: false});
-      test.setMediaConstraints([{video: true}], [{video: true}]);
+    // Two recv transceivers, one for each simulcast stream
+    offerer.addTransceiver('video', { direction: 'recvonly' });
+    offerer.addTransceiver('video', { direction: 'recvonly' });
 
-      test.chain.replace("PC_REMOTE_GUM", [
-        function PC_REMOTE_CANVAS_CAPTURESTREAM(test) {
-          emitter = new VideoFrameEmitter();
-          helper = new VideoStreamHelper();
-          test.pcRemote.attachLocalStream(emitter.stream());
-          emitter.start();
-        }
-      ]);
+    // One send transceiver, that will be used to send both simulcast streams
+    const emitter = new VideoFrameEmitter();
+    const videoStream = emitter.stream();
+    answerer.addTrack(videoStream.getVideoTracks()[0], videoStream);
+    emitter.start();
 
-      test.chain.insertAfter('PC_REMOTE_GET_OFFER', [
-        function PC_REMOTE_SET_RIDS(test) {
-          const senders = test.pcRemote._pc.getSenders();
-          is(senders.length, 1, "We have exactly one RTP sender");
-          const sender = senders[0];
-          ok(sender.track, "Sender has a track");
+    const offer = await offerer.createOffer();
 
-          return sender.setParameters({
-            encodings: [{ rid: "foo", maxBitrate: 40000 },
-                        { rid: "bar", maxBitrate: 40000, scaleResolutionDownBy: 2 }]
-          });
-        },
-        function PC_LOCAL_ADD_RIDS_TO_OFFER(test) {
-          // Create a dummy offer, and use it to set simulcast stuff on the
-          // offer we will actually be using.
-          return test.createOffer(test.pcRemote).then(offer => {
-            test._local_offer.sdp = sdputils.transferSimulcastProperties(
-                offer.sdp, test._local_offer.sdp);
-            info("Offer with RIDs: " + JSON.stringify(test._local_offer));
-            ok(test._local_offer.sdp.match(/a=simulcast:/), "Modified offer has simulcast");
-            ok(test._local_offer.sdp.match(/a=rid:foo/), "Modified offer has rid foo");
-            ok(test._local_offer.sdp.match(/a=rid:bar/), "Modified offer has rid bar");
-            ok(test._local_offer.sdp.match(/urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id/), "Modified offer has RID");
-          });
-        }
-      ]);
+    const mungedOffer = midToRid(offer.sdp);
+    info(`Transformed recv offer to simulcast: ${offer.sdp} to ${mungedOffer}`);
 
-      test.chain.insertAfter('PC_LOCAL_GET_ANSWER',[
-        function PC_LOCAL_REMOVE_SIMULCAST_ATTRS_FROM_ANSWER(test) {
-          test._remote_answer.sdp =
-            sdputils.removeSimulcastProperties(test._remote_answer.sdp);
-        }
-      ]);
+    await answerer.setRemoteDescription({type: 'offer', sdp: mungedOffer});
+    await offerer.setLocalDescription(offer);
 
-      // do this after set remote description so the MediaPipeline
-      // has been created.
-      test.chain.insertAfter('PC_LOCAL_SET_REMOTE_DESCRIPTION',[
-        function PC_LOCAL_SET_RTP_FIRST_RID(test) {
-          const extmap_id = test._local_offer.sdp.match(
-              "a=extmap:([0-9+])/recvonly urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id");
-          ok(extmap_id, "Local offer has extmap id for simulcast: " + extmap_id[1]);
-          // Cause pcLocal to filter out everything but RID "bar", only
-          // allowing one of the simulcast streams through.
-          addRIDExtension(test.pcLocal, extmap_id[1]);
-          selectRecvRID(test.pcLocal, "bar");
-        }
-      ]);
+    const rids = offerer.getTransceivers().map(t => t.mid);
+    is(rids.length, 2, 'Should have 2 mids in offer');
+    ok(rids[0] != '', 'First mid should be non-empty');
+    ok(rids[1] != '', 'Second mid should be non-empty');
+    info(`rids: ${JSON.stringify(rids)}`);
 
-      test.chain.append([
-        async function PC_LOCAL_WAIT_FOR_FRAMES() {
-          const vremote = test.pcLocal.remoteMediaElements[0];
-          ok(vremote, "Should have remote video element for pcLocal");
-          emitter.start();
-          await helper.checkVideoPlaying(vremote);
-          emitter.stop();
-        },
-        function PC_LOCAL_CHECK_SIZE_1() {
-          const vlocal = test.pcRemote.localMediaElements[0];
-          const vremote = test.pcLocal.remoteMediaElements[0];
-          ok(vlocal, "Should have local video element for pcRemote");
-          ok(vremote, "Should have remote video element for pcLocal");
-          is(vlocal.videoWidth, 50, "correct source width");
-          is(vlocal.videoHeight, 50, "correct source height");
-          is(vremote.videoWidth, 24,
-             "sink is 1/2 width of source, modulo our cropping algorithm");
-          is(vremote.videoHeight, 24,
-             "sink is 1/2 height of source, modulo our cropping algorithm");
-        },
-        function PC_LOCAL_SET_RTP_SECOND_RID(test) {
-          // Now, cause pcLocal to filter out everything but RID "foo", only
-          // allowing the other simulcast stream through.
-          selectRecvRID(test.pcLocal, "foo");
-        },
-        function PC_LOCAL_WAIT_FOR_SECOND_MEDIA_FLOW(test) {
-          return test.pcLocal.waitForMediaFlow();
-        },
-        async function PC_LOCAL_WAIT_FOR_FRAMES_2() {
-          const vremote = test.pcLocal.remoteMediaElements[0];
-          ok(vremote, "Should have remote video element for pcLocal");
-          emitter.start();
-          await helper.checkVideoPlaying(vremote);
-          emitter.stop();
-        },
-        // For some reason, even though we're getting a 24x24 stream, sometimes
-        // the resolution isn't updated on the video element on the first frame.
-        async function PC_LOCAL_WAIT_FOR_FRAMES_3() {
-          const vremote = test.pcLocal.remoteMediaElements[0];
-          ok(vremote, "Should have remote video element for pcLocal");
-          emitter.start();
-          await helper.checkVideoPlaying(vremote);
-          emitter.stop();
-        },
-        function PC_LOCAL_CHECK_SIZE_2() {
-          const vlocal = test.pcRemote.localMediaElements[0];
-          const vremote = test.pcLocal.remoteMediaElements[0];
-          ok(vlocal, "Should have local video element for pcRemote");
-          ok(vremote, "Should have remote video element for pcLocal");
-          is(vlocal.videoWidth, 50, "correct source width");
-          is(vlocal.videoHeight, 50, "correct source height");
-          is(vremote.videoWidth, 48,
-             "sink is same width as source, modulo our cropping algorithm");
-          is(vremote.videoHeight, 48,
-             "sink is same height as source, modulo our cropping algorithm");
-        },
-      ]);
+    const sender = answerer.getSenders()[0];
+    await sender.setParameters({
+        encodings: [
+            { rid: rids[0], maxBitrate: 40000 },
+            { rid: rids[1], maxBitrate: 40000, scaleResolutionDownBy: 2 }
+          ]
+    });
 
-      return test.run();
-  })
-  .catch(e => ok(false, "unexpected failure: " + e)));
+    const answer = await answerer.createAnswer();
+
+    const mungedAnswer = ridToMid(answer.sdp);
+    info(`Transformed send simulcast answer to multiple m-sections: ${answer.sdp} to ${mungedAnswer}`);
+    await offerer.setRemoteDescription({type: 'answer', sdp: mungedAnswer});
+    await answerer.setLocalDescription(answer);
+
+    is(metadataToBeLoaded.length, 2, 'Offerer should have gotten 2 ontrack events');
+    info('Waiting for 2 loadedmetadata events');
+    const videoElems = await Promise.all(metadataToBeLoaded);
+
+    const helper = new VideoStreamHelper();
+    info('Waiting for first video element to start playing');
+    await helper.checkVideoPlaying(videoElems[0]);
+    info('Waiting for second video element to start playing');
+    await helper.checkVideoPlaying(videoElems[1]);
+
+    is(videoElems[0].videoWidth, 48,
+       "sink is same width as source, modulo our cropping algorithm");
+    is(videoElems[0].videoHeight, 48,
+       "sink is same height as source, modulo our cropping algorithm");
+    is(videoElems[1].videoWidth, 24,
+       "sink is 1/2 width of source, modulo our cropping algorithm");
+    is(videoElems[1].videoHeight, 24,
+       "sink is 1/2 height of source, modulo our cropping algorithm");
+
+    emitter.stop();
+    videoStream.getVideoTracks()[0].stop();
+    offerer.close();
+    answerer.close();
+  });
 </script>
 </pre>
 </body>
diff --git a/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastAnswer_lowResFirst.html b/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastAnswer_lowResFirst.html
index 6c3c7b6accb2..2e9c81f07230 100644
--- a/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastAnswer_lowResFirst.html
+++ b/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastAnswer_lowResFirst.html
@@ -3,6 +3,8 @@
 <head>
   <script type="application/javascript" src="pc.js"></script>
   <script type="application/javascript" src="/tests/dom/canvas/test/captureStream_common.js"></script>
+  <script type="application/javascript" src="helpers_from_wpt/sdp.js"></script>
+  <script type="application/javascript" src="simulcast.js"></script>
 </head>
 <body>
 <pre id="test">
@@ -13,151 +15,90 @@
     visible: true
   });
 
-  function addRIDExtension(pc, extensionId) {
-    const receivers = pc._pc.getReceivers();
-    is(receivers.length, 1, "We have exactly one RTP receiver");
-    const receiver = receivers[0];
+  runNetworkTest(async () => {
+    await pushPrefs(
+        ['media.peerconnection.simulcast', true],
+        // 180Kbps was determined empirically, set well-higher than
+        // the 80Kbps+overhead needed for the two simulcast streams.
+        // 100Kbps was apparently too low.
+        ['media.peerconnection.video.min_bitrate_estimate', 180*1000]);
 
-    SpecialPowers.wrap(receiver).mozAddRIDExtension(extensionId);
-  }
 
-  function selectRecvRID(pc, rid) {
-    const receivers = pc._pc.getReceivers();
-    is(receivers.length, 1, "We have exactly one RTP receiver");
-    const receiver = receivers[0];
+    const offerer = new RTCPeerConnection();
+    const answerer = new RTCPeerConnection();
 
-    SpecialPowers.wrap(receiver).mozAddRIDFilter(rid);
-  }
+    const add = (pc, can, failed) => can && pc.addIceCandidate(can).catch(failed);
+    offerer.onicecandidate = e => add(answerer, e.candidate, generateErrorCallback());
+    answerer.onicecandidate = e => add(offerer, e.candidate, generateErrorCallback());
 
-  runNetworkTest(() =>
-    pushPrefs(['media.peerconnection.simulcast', true],
-              // 180Kbps was determined empirically, set well-higher than
-              // the 80Kbps+overhead needed for the two simulcast streams.
-              // 100Kbps was apparently too low.
-              ['media.peerconnection.video.min_bitrate_estimate', 180*1000]).then(() => {
-      let emitter, helper;
+    const metadataToBeLoaded = [];
+    offerer.ontrack = (e) => {
+      metadataToBeLoaded.push(getPlaybackWithLoadedMetadata(e.track));
+    };
 
-      test = new PeerConnectionTest({bundle: false});
-      test.setMediaConstraints([{video: true}], [{video: true}]);
+    // Two recv transceivers, one for each simulcast stream
+    offerer.addTransceiver('video', { direction: 'recvonly' });
+    offerer.addTransceiver('video', { direction: 'recvonly' });
 
-      test.chain.replace("PC_REMOTE_GUM", [
-        function PC_REMOTE_CANVAS_CAPTURESTREAM(test) {
-          emitter = new VideoFrameEmitter();
-          helper = new VideoStreamHelper();
-          test.pcRemote.attachLocalStream(emitter.stream());
-          emitter.start();
-        }
-      ]);
+    // One send transceiver, that will be used to send both simulcast streams
+    const emitter = new VideoFrameEmitter();
+    const videoStream = emitter.stream();
+    answerer.addTrack(videoStream.getVideoTracks()[0], videoStream);
+    emitter.start();
 
-      test.chain.insertAfter('PC_REMOTE_GET_OFFER', [
-        function PC_REMOTE_SET_RIDS(test) {
-          const senders = test.pcRemote._pc.getSenders();
-          is(senders.length, 1, "We have exactly one RTP sender");
-          const sender = senders[0];
-          ok(sender.track, "Sender has a track");
+    const offer = await offerer.createOffer();
 
-          return sender.setParameters({
-            encodings: [{ rid: "foo", maxBitrate: 40000, scaleResolutionDownBy: 2 },
-                        { rid: "bar", maxBitrate: 40000 }]
-          });
-        },
-        function PC_LOCAL_ADD_RIDS_TO_OFFER(test) {
-          // Create a dummy offer, and use it to set simulcast stuff on the
-          // offer we will actually be using.
-          return test.createOffer(test.pcRemote).then(offer => {
-            test._local_offer.sdp = sdputils.transferSimulcastProperties(
-                offer.sdp, test._local_offer.sdp);
-            info("Offer with RIDs: " + JSON.stringify(test._local_offer));
-            ok(test._local_offer.sdp.match(/a=simulcast:/), "Modified offer has simulcast");
-            ok(test._local_offer.sdp.match(/a=rid:foo/), "Modified offer has rid foo");
-            ok(test._local_offer.sdp.match(/a=rid:bar/), "Modified offer has rid bar");
-            ok(test._local_offer.sdp.match(/urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id/), "Modified offer has RID");
-          });
-        }
-      ]);
+    const mungedOffer = midToRid(offer.sdp);
+    info(`Transformed recv offer to simulcast: ${offer.sdp} to ${mungedOffer}`);
 
-      test.chain.insertAfter('PC_LOCAL_GET_ANSWER',[
-        function PC_LOCAL_REMOVE_SIMULCAST_ATTRS_FROM_ANSWER(test) {
-          test._remote_answer.sdp =
-            sdputils.removeSimulcastProperties(test._remote_answer.sdp);
-        }
-      ]);
+    await answerer.setRemoteDescription({type: 'offer', sdp: mungedOffer});
+    await offerer.setLocalDescription(offer);
 
-      // do this after set remote description so the MediaPipeline
-      // has been created.
-      test.chain.insertAfter('PC_LOCAL_SET_REMOTE_DESCRIPTION',[
-        function PC_LOCAL_SET_RTP_FIRST_RID(test) {
-          const extmap_id = test._local_offer.sdp.match(
-              "a=extmap:([0-9+])/recvonly urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id");
-          ok(extmap_id, "Local offer has extmap id for simulcast: " + extmap_id[1]);
-          // Cause pcLocal to filter out everything but RID "bar", only
-          // allowing one of the simulcast streams through.
-          addRIDExtension(test.pcLocal, extmap_id[1]);
-          selectRecvRID(test.pcLocal, "bar");
-        }
-      ]);
+    const rids = offerer.getTransceivers().map(t => t.mid);
+    is(rids.length, 2, 'Should have 2 mids in offer');
+    ok(rids[0] != '', 'First mid should be non-empty');
+    ok(rids[1] != '', 'Second mid should be non-empty');
+    info(`rids: ${JSON.stringify(rids)}`);
 
-      test.chain.append([
-        async function PC_LOCAL_WAIT_FOR_FRAMES() {
-          const vremote = test.pcLocal.remoteMediaElements[0];
-          ok(vremote, "Should have remote video element for pcLocal");
-          emitter.start();
-          await helper.checkVideoPlaying(vremote);
-          emitter.stop();
-        },
-        function PC_LOCAL_CHECK_SIZE_1() {
-          const vlocal = test.pcRemote.localMediaElements[0];
-          const vremote = test.pcLocal.remoteMediaElements[0];
-          ok(vlocal, "Should have local video element for pcRemote");
-          ok(vremote, "Should have remote video element for pcLocal");
-          is(vlocal.videoWidth, 50, "correct source width");
-          is(vlocal.videoHeight, 50, "correct source height");
-          is(vremote.videoWidth, 48,
-             "sink is same width as source, modulo our cropping algorithm");
-          is(vremote.videoHeight, 48,
-             "sink is same height as source, modulo our cropping algorithm");
-        },
-        function PC_LOCAL_SET_RTP_SECOND_RID(test) {
-          // Now, cause pcLocal to filter out everything but RID "foo", only
-          // allowing the other simulcast stream through.
-          selectRecvRID(test.pcLocal, "foo");
-        },
-        function PC_LOCAL_WAIT_FOR_SECOND_MEDIA_FLOW(test) {
-          return test.pcLocal.waitForMediaFlow();
-        },
-        async function PC_LOCAL_WAIT_FOR_FRAMES_2() {
-          const vremote = test.pcLocal.remoteMediaElements[0];
-          ok(vremote, "Should have remote video element for pcLocal");
-          emitter.start();
-          await helper.checkVideoPlaying(vremote);
-          emitter.stop();
-        },
-        // For some reason, even though we're getting a 24x24 stream, sometimes
-        // the resolution isn't updated on the video element on the first frame.
-        async function PC_LOCAL_WAIT_FOR_FRAMES_3() {
-          const vremote = test.pcLocal.remoteMediaElements[0];
-          ok(vremote, "Should have remote video element for pcLocal");
-          emitter.start();
-          await helper.checkVideoPlaying(vremote);
-          emitter.stop();
-        },
-        function PC_LOCAL_CHECK_SIZE_2() {
-          const vlocal = test.pcRemote.localMediaElements[0];
-          const vremote = test.pcLocal.remoteMediaElements[0];
-          ok(vlocal, "Should have local video element for pcRemote");
-          ok(vremote, "Should have remote video element for pcLocal");
-          is(vlocal.videoWidth, 50, "correct source width");
-          is(vlocal.videoHeight, 50, "correct source height");
-          is(vremote.videoWidth, 24,
-             "sink is 1/2 width of source, modulo our cropping algorithm");
-          is(vremote.videoHeight, 24,
-             "sink is 1/2 height of source, modulo our cropping algorithm");
-        },
-      ]);
+    const sender = answerer.getSenders()[0];
+    sender.setParameters({
+        encodings: [
+            { rid: rids[0], maxBitrate: 40000, scaleResolutionDownBy: 2 },
+            { rid: rids[1], maxBitrate: 40000 }
+          ]
+    });
 
-      return test.run();
-  })
-  .catch(e => ok(false, "unexpected failure: " + e)));
+    const answer = await answerer.createAnswer();
+
+    const mungedAnswer = ridToMid(answer.sdp);
+    info(`Transformed send simulcast answer to multiple m-sections: ${answer.sdp} to ${mungedAnswer}`);
+    await offerer.setRemoteDescription({type: 'answer', sdp: mungedAnswer});
+    await answerer.setLocalDescription(answer);
+
+    is(metadataToBeLoaded.length, 2, 'Offerer should have gotten 2 ontrack events');
+    info('Waiting for 2 loadedmetadata events');
+    const videoElems = await Promise.all(metadataToBeLoaded);
+
+    const helper = new VideoStreamHelper();
+    info('Waiting for first video element to start playing');
+    await helper.checkVideoPlaying(videoElems[0]);
+    info('Waiting for second video element to start playing');
+    await helper.checkVideoPlaying(videoElems[1]);
+
+    is(videoElems[1].videoWidth, 48,
+       "sink is same width as source, modulo our cropping algorithm");
+    is(videoElems[1].videoHeight, 48,
+       "sink is same height as source, modulo our cropping algorithm");
+    is(videoElems[0].videoWidth, 24,
+       "sink is 1/2 width of source, modulo our cropping algorithm");
+    is(videoElems[0].videoHeight, 24,
+       "sink is 1/2 height of source, modulo our cropping algorithm");
+
+    emitter.stop();
+    videoStream.getVideoTracks()[0].stop();
+    offerer.close();
+    answerer.close();
+  });
 </script>
 </pre>
 </body>
diff --git a/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastOddResolution.html b/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastOddResolution.html
index b42683a3d710..a28bb8c6a5ad 100644
--- a/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastOddResolution.html
+++ b/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastOddResolution.html
@@ -3,6 +3,8 @@
 <head>
   <script type="application/javascript" src="pc.js"></script>
   <script type="application/javascript" src="/tests/dom/canvas/test/captureStream_common.js"></script>
+  <script type="application/javascript" src="helpers_from_wpt/sdp.js"></script>
+  <script type="application/javascript" src="simulcast.js"></script>
 </head>
 <body>
 <pre id="test">
@@ -13,196 +15,143 @@
     visible: true
   });
 
-  const encodings = [{ rid: "foo", maxBitrate: 40000, scaleResolutionDownBy: 1.9 },
-                     { rid: "bar", maxBitrate: 40000, scaleResolutionDownBy: 3.5 },
-                     { rid: "baz", maxBitrate: 40000, scaleResolutionDownBy: 17.8 }];
-
-  function addRIDExtension(pc, extensionId) {
-    const receivers = pc._pc.getReceivers();
-    is(receivers.length, 1, "We have exactly one RTP receiver");
-    const receiver = receivers[0];
-
-    SpecialPowers.wrap(receiver).mozAddRIDExtension(extensionId);
-  }
-
-  function selectRecvRID(pc, rid) {
-    const receivers = pc._pc.getReceivers();
-    is(receivers.length, 1, "We have exactly one RTP receiver");
-    const receiver = receivers[0];
-
-    SpecialPowers.wrap(receiver).mozAddRIDFilter(rid);
-  }
-
-  async function changeSourceResolution(test, emitter, width, height) {
-    info(`Changing source resolution to ${width}x${height}`);
-    emitter.size(width, height);
-    emitter.start();
-    await Promise.all([
-        haveEvent(test.pcRemote.localMediaElements[0], "resize"),
-        haveEvent(test.pcLocal.remoteMediaElements[0], "resize"),
-    ]);
-    emitter.stop();
-    info("Source resolution changed");
-  }
-
-  async function setParameters(test, emitter, encodings) {
-    info(`Setting parameters to ${JSON.stringify(encodings)}`);
-    emitter.start();
-    await test.pcRemote._pc.getSenders()[0].setParameters({encodings});
-    await haveEvent(test.pcLocal.remoteMediaElements[0], "resize");
-    emitter.stop();
-		info("Parameters set");
-	}
-
-  async function checkResolution(test, emitter, rid) {
-    const vlocal = test.pcRemote.localMediaElements[0];
-    const vremote = test.pcLocal.remoteMediaElements[0];
-
-    info(`Changing to rid ${rid}`);
-    selectRecvRID(test.pcLocal, rid);
-    emitter.start();
-    await haveEvent(vremote, "resize");
-    emitter.stop();
-
-    const srcWidth = vlocal.videoWidth;
-    const srcHeight = vlocal.videoHeight;
-    info(`Source resolution is ${srcWidth}x${srcHeight}`);
-
-    const scaleDownBy = encodings.find(({rid: r}) => r == rid).scaleResolutionDownBy;
-    const expectedWidth = srcWidth / scaleDownBy;
-    const expectedHeight = srcHeight / scaleDownBy;
-    const margin = srcWidth * 0.1;
-    const width = vremote.videoWidth;
-    const height = vremote.videoHeight;
-    ok(width >= expectedWidth - margin && width <= expectedWidth + margin,
-      `Width ${width} should be within 10% of ${expectedWidth} for rid '${rid}'`);
-    ok(height >= expectedHeight - margin && height <= expectedHeight + margin,
-      `Height ${height} should be within 10% of ${expectedHeight} for rid '${rid}'`);
-  }
-
-  async function checkResolutions(test, emitter) {
-    const vremote = test.pcLocal.remoteMediaElements[0];
-
-    // Start by making sure we're not on foo (first default) or
-    // baz (subsequent default), thus getting resize events.
-    selectRecvRID(test.pcLocal, "bar");
-    emitter.start();
-    await haveEvent(vremote, "resize");
-    emitter.stop();
-
-    await checkResolution(test, emitter, "foo");
-    await checkResolution(test, emitter, "bar");
-    await checkResolution(test, emitter, "baz");
-  }
-
   runNetworkTest(async () => {
-    await pushPrefs(['media.peerconnection.simulcast', true],
-                    ['media.peerconnection.video.lock_scaling', true],
-                    // 240Kbps was determined empirically
-                    ['media.peerconnection.video.min_bitrate_estimate', 240*1000]);
+    const helper = new VideoStreamHelper();
+    const emitter = new VideoFrameEmitter(helper.green, helper.red, 705, 528);
 
-    let emitter, helper;
+    async function checkVideoElement(senderElement, receiverElement, encoding) {
+      info(`Waiting for receiver video element ${encoding.rid} to start playing`);
+      await helper.checkVideoPlaying(receiverElement);
+      const srcWidth = senderElement.videoWidth;
+      const srcHeight = senderElement.videoHeight;
+      info(`Source resolution is ${srcWidth}x${srcHeight}`);
 
-    test = new PeerConnectionTest({bundle: false});
-    test.setMediaConstraints([{video: true}], [{video: true}]);
+      const scaleDownBy = encoding.scaleResolutionDownBy;
+      const expectedWidth = srcWidth / scaleDownBy;
+      const expectedHeight = srcHeight / scaleDownBy;
+      const margin = srcWidth * 0.1;
+      const width = receiverElement.videoWidth;
+      const height = receiverElement.videoHeight;
+      const rid = encoding.rid;
+      ok(width >= expectedWidth - margin && width <= expectedWidth + margin,
+        `Width ${width} should be within 10% of ${expectedWidth} for rid '${rid}'`);
+      ok(height >= expectedHeight - margin && height <= expectedHeight + margin,
+        `Height ${height} should be within 10% of ${expectedHeight} for rid '${rid}'`);
+    }
 
-    test.chain.replace("PC_REMOTE_GUM", [
-      function PC_REMOTE_CANVAS_CAPTURESTREAM(test) {
-        helper = new VideoStreamHelper();
-        emitter = new VideoFrameEmitter(helper.green, helper.red, 705, 528);
-        test.pcRemote.attachLocalStream(emitter.stream());
-        // Don't start the emitter yet. Only do that when we're able to set rid filters.
+    async function checkVideoElements(senderElement, receiverElements, encodings) {
+      is(receiverElements.length, encodings.length, 'Number of video elements should match number of encodings');
+      info('Waiting for sender video element to start playing');
+      await helper.checkVideoPlaying(senderElement);
+      for (let i = 0; i < encodings.length; i++) {
+        await checkVideoElement(senderElement, receiverElements[i], encodings[i]);
       }
-    ]);
+    }
 
-    test.chain.insertAfter('PC_REMOTE_GET_OFFER', [
-      function PC_REMOTE_SET_RIDS(test) {
-        const senders = test.pcRemote._pc.getSenders();
-        is(senders.length, 1, "We have exactly one RTP sender");
-        const sender = senders[0];
-        ok(sender.track, "Sender has a track");
+    async function waitForResizeEvents(elements) {
+      return Promise.all(elements.map(elem => haveEvent(elem, 'resize')));
+    }
 
-        return sender.setParameters({encodings});
-      },
-      async function PC_LOCAL_ADD_RIDS_TO_OFFER(test) {
-        // Create a dummy offer, and use it to set simulcast stuff on the
-        // offer we will actually be using.
-        let offer = await test.createOffer(test.pcRemote);
-        test._local_offer.sdp = sdputils.transferSimulcastProperties(
-            offer.sdp, test._local_offer.sdp);
-        info(`Offer with RIDs: ${JSON.stringify(test._local_offer)}`);
-        ok(test._local_offer.sdp.match(/a=simulcast:/), "Modified offer has simulcast");
-        ok(test._local_offer.sdp.match(/a=rid:foo/), "Modified offer has rid foo");
-        ok(test._local_offer.sdp.match(/a=rid:bar/), "Modified offer has rid bar");
-        ok(test._local_offer.sdp.match(/a=rid:baz/), "Modified offer has rid bar");
-        ok(test._local_offer.sdp.match(/urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id/), "Modified offer has RID");
-      }
-    ]);
+    const encodings = [{ rid: "0", maxBitrate: 40000, scaleResolutionDownBy: 1.9 },
+                       { rid: "1", maxBitrate: 40000, scaleResolutionDownBy: 3.5 },
+                       { rid: "2", maxBitrate: 40000, scaleResolutionDownBy: 17.8 }];
 
-    test.chain.insertAfter('PC_LOCAL_GET_ANSWER',[
-      function PC_LOCAL_REMOVE_SIMULCAST_ATTRS_FROM_ANSWER(test) {
-        test._remote_answer.sdp =
-          sdputils.removeSimulcastProperties(test._remote_answer.sdp);
-      }
-    ]);
+    await pushPrefs(
+        ['media.peerconnection.simulcast', true],
+        // 180Kbps was determined empirically, set well-higher than
+        // the 80Kbps+overhead needed for the two simulcast streams.
+        // 100Kbps was apparently too low.
+        ['media.peerconnection.video.min_bitrate_estimate', 180*1000]);
 
-    // do this after set remote description so the MediaPipeline
-    // has been created.
-    test.chain.insertAfter('PC_LOCAL_SET_REMOTE_DESCRIPTION',[
-      function PC_LOCAL_SET_RTP_FIRST_RID(test) {
-        info(`local offer: ${test._local_offer.sdp}`);
-        const extmap_id = test._local_offer.sdp.match(
-            "a=extmap:([0-9+])/recvonly urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id");
-        ok(extmap_id, `Original answer has extmap id for simulcast: ${extmap_id[1]}`);
-        // Cause pcLocal to filter out everything but RID "foo", only
-        // allowing one of the simulcast streams through.
-        addRIDExtension(test.pcLocal, extmap_id[1]);
-        selectRecvRID(test.pcLocal, "foo");
-        emitter.start();
-      },
-      function SETUP_RESIZE_LISTENERS(test) {
-        for(const elem of [...test.pcRemote.localMediaElements,
-                           ...test.pcLocal.remoteMediaElements,
-                          ]) {
-          elem.addEventListener("resize",
-            () => info(`element ${elem.id} resized to ${elem.videoWidth}x${elem.videoHeight}`));
-        }
-      },
-    ]);
 
-    test.chain.append([
-      async function PC_LOCAL_CHECK_INITIAL_SIZES() {
-        await checkResolutions(test, emitter);
-      },
-      async function PC_LOCAL_CHANGE_SRC_1() {
-        await changeSourceResolution(test, emitter, 1280, 720);
-        await checkResolutions(test, emitter);
-      },
-      async function PC_LOCAL_CHANGE_PARAMS_2() {
-        encodings.find(({rid}) => rid == "foo").scaleResolutionDownBy = 1;
-        encodings.find(({rid}) => rid == "bar").scaleResolutionDownBy = 2;
-        encodings.find(({rid}) => rid == "baz").scaleResolutionDownBy = 3;
-        await setParameters(test, emitter, encodings);
-        await checkResolutions(test, emitter);
-      },
-      async function PC_LOCAL_CHANGE_PARAMS_3() {
-        encodings.find(({rid}) => rid == "foo").scaleResolutionDownBy = 6;
-        encodings.find(({rid}) => rid == "bar").scaleResolutionDownBy = 5;
-        encodings.find(({rid}) => rid == "baz").scaleResolutionDownBy = 4;
-        await setParameters(test, emitter, encodings);
-        await checkResolutions(test, emitter);
-      },
-      async function PC_LOCAL_CHANGE_PARAMS_4() {
-        encodings.find(({rid}) => rid == "foo").scaleResolutionDownBy = 4;
-        encodings.find(({rid}) => rid == "bar").scaleResolutionDownBy = 1;
-        encodings.find(({rid}) => rid == "baz").scaleResolutionDownBy = 2;
-        await setParameters(test, emitter, encodings);
-        await checkResolutions(test, emitter);
-      },
-    ]);
+    const offerer = new RTCPeerConnection();
+    const answerer = new RTCPeerConnection();
 
-    await test.run();
+    const add = (pc, can, failed) => can && pc.addIceCandidate(can).catch(failed);
+    offerer.onicecandidate = e => add(answerer, e.candidate, generateErrorCallback());
+    answerer.onicecandidate = e => add(offerer, e.candidate, generateErrorCallback());
+
+    const metadataToBeLoaded = [];
+    answerer.ontrack = (e) => {
+      metadataToBeLoaded.push(getPlaybackWithLoadedMetadata(e.track));
+    };
+
+    // One send transceiver, that will be used to send both simulcast streams
+    const videoStream = emitter.stream();
+    offerer.addTrack(videoStream.getVideoTracks()[0], videoStream);
+    const senderElement = document.createElement('video');
+    senderElement.autoplay = true;
+    senderElement.srcObject = videoStream;
+    senderElement.id = videoStream.id
+
+    const sender = offerer.getSenders()[0];
+    sender.setParameters({encodings});
+
+    const offer = await offerer.createOffer();
+
+    const mungedOffer = ridToMid(offer.sdp);
+    info(`Transformed send simulcast offer to multiple m-sections: ${offer.sdp} to ${mungedOffer}`);
+
+    await answerer.setRemoteDescription({type: 'offer', sdp: mungedOffer});
+    await offerer.setLocalDescription(offer);
+
+    const rids = answerer.getTransceivers().map(t => t.mid);
+    is(rids.length, 3, 'Should have 3 mids in offer');
+    ok(rids[0], 'First mid should be non-empty');
+    ok(rids[1], 'Second mid should be non-empty');
+    ok(rids[2], 'Third mid should be non-empty');
+    info(`rids: ${JSON.stringify(rids)}`);
+
+    const answer = await answerer.createAnswer();
+
+    const mungedAnswer = midToRid(answer.sdp);
+    info(`Transformed recv answer to simulcast: ${answer.sdp} to ${mungedAnswer}`);
+    await offerer.setRemoteDescription({type: 'answer', sdp: mungedAnswer});
+    await answerer.setLocalDescription(answer);
+
+    is(metadataToBeLoaded.length, 3, 'Offerer should have gotten 3 ontrack events');
+    emitter.start();
+    info('Waiting for 3 loadedmetadata events');
+    const videoElems = await Promise.all(metadataToBeLoaded);
+    await checkVideoElements(senderElement, videoElems, encodings);
+    emitter.stop();
+
+    info(`Changing source resolution to 1280x720`);
+    emitter.size(1280, 720);
+    emitter.start();
+    await waitForResizeEvents([senderElement, ...videoElems]);
+    await checkVideoElements(senderElement, videoElems, encodings);
+
+    encodings[0].scaleResolutionDownBy = 1;
+    encodings[1].scaleResolutionDownBy = 2;
+    encodings[2].scaleResolutionDownBy = 3;
+    info(`Changing encodings to ${JSON.stringify(encodings)}`);
+    await sender.setParameters({encodings});
+    await waitForResizeEvents(videoElems);
+    await checkVideoElements(senderElement, videoElems, encodings);
+
+    encodings[0].scaleResolutionDownBy = 6;
+    encodings[1].scaleResolutionDownBy = 5;
+    encodings[2].scaleResolutionDownBy = 4;
+    info(`Changing encodings to ${JSON.stringify(encodings)}`);
+    await sender.setParameters({encodings});
+    await waitForResizeEvents(videoElems);
+    await checkVideoElements(senderElement, videoElems, encodings);
+
+    encodings[0].scaleResolutionDownBy = 4;
+    encodings[1].scaleResolutionDownBy = 1;
+    encodings[2].scaleResolutionDownBy = 2;
+    info(`Changing encodings to ${JSON.stringify(encodings)}`);
+    await sender.setParameters({encodings});
+    await waitForResizeEvents(videoElems);
+    await checkVideoElements(senderElement, videoElems, encodings);
+
+    emitter.stop();
+    videoStream.getVideoTracks()[0].stop();
+    offerer.close();
+    answerer.close();
   });
+
 </script>
 </pre>
 </body>
diff --git a/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastOffer.html b/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastOffer.html
index 287e810f6011..9bbef3347c4e 100644
--- a/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastOffer.html
+++ b/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastOffer.html
@@ -4,6 +4,8 @@
   <script type="application/javascript" src="pc.js"></script>
   <script type="application/javascript" src="parser_rtp.js"></script>
   <script type="application/javascript" src="/tests/dom/canvas/test/captureStream_common.js"></script>
+  <script type="application/javascript" src="helpers_from_wpt/sdp.js"></script>
+  <script type="application/javascript" src="simulcast.js"></script>
 </head>
 <body>
 <pre id="test">
@@ -14,172 +16,85 @@
     visible: true
   });
 
-  function addRIDExtension(pc, extensionId) {
-    const receivers = pc._pc.getReceivers();
-    is(receivers.length, 1, "We have exactly one RTP receiver");
-    const receiver = receivers[0];
-
-    SpecialPowers.wrap(receiver).mozAddRIDExtension(extensionId);
-  }
-
-  function selectRecvRID(pc, rid) {
-    const receivers = pc._pc.getReceivers();
-    is(receivers.length, 1, "We have exactly one RTP receiver");
-    const receiver = receivers[0];
-
-    SpecialPowers.wrap(receiver).mozAddRIDFilter(rid);
-  }
-
   runNetworkTest(async () => {
     await pushPrefs(
-      ['media.peerconnection.simulcast', true],
-      // 180Kbps was determined empirically, set well-higher than
-      // the 80Kbps+overhead needed for the two simulcast streams.
-      // 100Kbps was apparently too low.
-      ['media.peerconnection.video.min_bitrate_estimate', 180*1000],
-    );
+        ['media.peerconnection.simulcast', true],
+        // 180Kbps was determined empirically, set well-higher than
+        // the 80Kbps+overhead needed for the two simulcast streams.
+        // 100Kbps was apparently too low.
+        ['media.peerconnection.video.min_bitrate_estimate', 180*1000]);
 
-    let emitter, helper;
 
-    const test = new PeerConnectionTest({bundle: false});
-    test.setMediaConstraints([{video: true}], []);
+    const offerer = new RTCPeerConnection();
+    const answerer = new RTCPeerConnection();
 
-    test.chain.replace("PC_LOCAL_GUM", [
-      function PC_LOCAL_CANVAS_CAPTURESTREAM(test) {
-        emitter = new VideoFrameEmitter();
-        helper = new VideoStreamHelper();
-        test.pcLocal.attachLocalStream(emitter.stream());
-        emitter.start();
-      }
-    ]);
+    const add = (pc, can, failed) => can && pc.addIceCandidate(can).catch(failed);
+    offerer.onicecandidate = e => add(answerer, e.candidate, generateErrorCallback());
+    answerer.onicecandidate = e => add(offerer, e.candidate, generateErrorCallback());
 
-    test.chain.insertBefore('PC_LOCAL_CREATE_OFFER', [
-      function PC_LOCAL_SET_RIDS(test) {
-        const senders = test.pcLocal._pc.getSenders();
-        is(senders.length, 1, "We have exactly one RTP sender");
-        const sender = senders[0];
-        ok(sender.track, "Sender has a track");
+    const metadataToBeLoaded = [];
+    answerer.ontrack = (e) => {
+      metadataToBeLoaded.push(getPlaybackWithLoadedMetadata(e.track));
+    };
 
-        return sender.setParameters({
-          encodings: [{ rid: "foo", maxBitrate: 40000 },
-                      { rid: "bar", maxBitrate: 40000, scaleResolutionDownBy: 2 }]
-        });
-      }
-    ]);
+    // One send transceiver, that will be used to send both simulcast streams
+    const emitter = new VideoFrameEmitter();
+    const videoStream = emitter.stream();
+    offerer.addTrack(videoStream.getVideoTracks()[0], videoStream);
+    emitter.start();
 
-    test.chain.insertAfter('PC_LOCAL_GET_ANSWER', [
-      function PC_LOCAL_ADD_RIDS_TO_ANSWER(test) {
-        test._remote_answer.sdp = sdputils.transferSimulcastProperties(
-          test.originalOffer.sdp, test._remote_answer.sdp);
-        info("Answer with RIDs: " + JSON.stringify(test._remote_answer));
-        ok(test._remote_answer.sdp.match(/a=simulcast:/), "Modified answer has simulcast");
-        ok(test._remote_answer.sdp.match(/a=rid:foo/), "Modified answer has rid foo");
-        ok(test._remote_answer.sdp.match(/a=rid:bar/), "Modified answer has rid bar");
-        ok(test._remote_answer.sdp.match(/urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id/), "Modified answer has RID");
-      }
-    ]);
+    const sender = offerer.getSenders()[0];
+    sender.setParameters({
+        encodings: [
+            { rid: '0', maxBitrate: 40000 },
+            { rid: '1', maxBitrate: 40000, scaleResolutionDownBy: 2 }
+          ]
+    });
 
-    // For storing the rid extension so it can be checked in the RTP
-    let ridExtensionId = 0;
+    const offer = await offerer.createOffer();
 
-    // do this after set local description so the MediaPipeline
-    // has been created.
-    test.chain.insertAfter('PC_REMOTE_SET_LOCAL_DESCRIPTION',[
-      function PC_REMOTE_SET_RTP_FIRST_RID(test) {
-        const extmap_id = test.originalOffer.sdp.match(
-            "a=extmap:([0-9+])/sendonly urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id");
-        ok(extmap_id, "Original offer has extmap id for simulcast: " + extmap_id[1]);
-        ridExtensionId = extmap_id[1];
-        // Cause pcRemote to filter out everything but RID "foo", only
-        // allowing one of the simulcast streams through.
-        addRIDExtension(test.pcRemote, extmap_id[1]);
-        selectRecvRID(test.pcRemote, "foo");
-      }
-    ]);
+    const mungedOffer = ridToMid(offer.sdp);
+    info(`Transformed send simulcast offer to multiple m-sections: ${offer.sdp} to ${mungedOffer}`);
 
-    let getRtpPacket = (pc) => {
-      pc.mozEnablePacketDump(0, "rtp", false);
-      return new Promise((res, rej) =>
-        pc.mozSetPacketCallback((...args) => {
-          res([...args]);
-          pc.mozSetPacketCallback(() => {});
-          pc.mozDisablePacketDump(0, "rtp", false);
-        })
-      );
-    }
+    await answerer.setRemoteDescription({type: 'offer', sdp: mungedOffer});
+    await offerer.setLocalDescription(offer);
 
-    test.chain.insertBefore('PC_REMOTE_WAIT_FOR_MEDIA_FLOW', [
-        async function PC_REMOTE_CHECK_RID_IN_RTP() {
-          let pc = SpecialPowers.wrap(test.pcRemote._pc);
-          let [level, type, sending, data] =  await getRtpPacket(pc);
-          let extensions = ParseRtpPacket(data).header.extensions;
-          ok(ridExtensionId, "RID extension ID has been extracted from SDP");
-          let ridExt = extensions.find(e => e.id == ridExtensionId);
-          ok(ridExt, "RID is present in RTP.");
-          is(new TextDecoder('utf-8').decode(ridExt.data), "foo",
-             "RID is 'foo'.");
-        }
-    ]);
+    const rids = answerer.getTransceivers().map(t => t.mid);
+    is(rids.length, 2, 'Should have 2 mids in offer');
+    ok(rids[0] != '', 'First mid should be non-empty');
+    ok(rids[1] != '', 'Second mid should be non-empty');
+    info(`rids: ${JSON.stringify(rids)}`);
 
-    test.chain.append([
-      async function PC_REMOTE_WAIT_FOR_FRAMES() {
-        const vremote = test.pcRemote.remoteMediaElements[0];
-        ok(vremote, "Should have remote video element for pcRemote");
-        emitter.start();
-        await helper.checkVideoPlaying(vremote);
-        emitter.stop();
-      },
-      function PC_REMOTE_CHECK_SIZE_1() {
-        const vlocal = test.pcLocal.localMediaElements[0];
-        const vremote = test.pcRemote.remoteMediaElements[0];
-        ok(vlocal, "Should have local video element for pcLocal");
-        ok(vremote, "Should have remote video element for pcRemote");
-        is(vlocal.videoWidth, 50, "correct source width");
-        is(vlocal.videoHeight, 50, "correct source height");
-        is(vremote.videoWidth, 48,
-           "sink is same width as source, modulo our cropping algorithm");
-        is(vremote.videoHeight, 48,
-           "sink is same height as source, modulo our cropping algorithm");
-      },
-      function PC_REMOTE_SET_RTP_SECOND_RID(test) {
-        // Now, cause pcRemote to filter out everything but RID "bar", only
-        // allowing the other simulcast stream through.
-        selectRecvRID(test.pcRemote, "bar");
-      },
-      function PC_REMOTE_WAIT_FOR_SECOND_MEDIA_FLOW(test) {
-        return test.pcRemote.waitForMediaFlow();
-      },
-      async function PC_REMOTE_WAIT_FOR_FRAMES_2() {
-        const vremote = test.pcRemote.remoteMediaElements[0];
-        ok(vremote, "Should have remote video element for pcRemote");
-        emitter.start();
-        await helper.checkVideoPlaying(vremote);
-        emitter.stop();
-      },
-      // For some reason, even though we're getting a 25x25 stream, sometimes
-      // the resolution isn't updated on the video element on the first frame.
-      async function PC_REMOTE_WAIT_FOR_FRAMES_3() {
-        const vremote = test.pcRemote.remoteMediaElements[0];
-        ok(vremote, "Should have remote video element for pcRemote");
-        emitter.start();
-        await helper.checkVideoPlaying(vremote);
-        emitter.stop();
-      },
-      function PC_REMOTE_CHECK_SIZE_2() {
-        const vlocal = test.pcLocal.localMediaElements[0];
-        const vremote = test.pcRemote.remoteMediaElements[0];
-        ok(vlocal, "Should have local video element for pcLocal");
-        ok(vremote, "Should have remote video element for pcRemote");
-        is(vlocal.videoWidth, 50, "correct source width");
-        is(vlocal.videoHeight, 50, "correct source height");
-        is(vremote.videoWidth, 24,
-           "sink is 1/2 width of source, modulo our cropping algorithm");
-        is(vremote.videoHeight, 24,
-           "sink is 1/2 height of source, modulo our cropping algorithm");
-      },
-    ]);
+    const answer = await answerer.createAnswer();
 
-    await test.run();
+    const mungedAnswer = midToRid(answer.sdp);
+    info(`Transformed recv answer to simulcast: ${answer.sdp} to ${mungedAnswer}`);
+    await offerer.setRemoteDescription({type: 'answer', sdp: mungedAnswer});
+    await answerer.setLocalDescription(answer);
+
+    is(metadataToBeLoaded.length, 2, 'Offerer should have gotten 2 ontrack events');
+    info('Waiting for 2 loadedmetadata events');
+    const videoElems = await Promise.all(metadataToBeLoaded);
+
+    const helper = new VideoStreamHelper();
+    info('Waiting for first video element to start playing');
+    await helper.checkVideoPlaying(videoElems[0]);
+    info('Waiting for second video element to start playing');
+    await helper.checkVideoPlaying(videoElems[1]);
+
+    is(videoElems[0].videoWidth, 48,
+       "sink is same width as source, modulo our cropping algorithm");
+    is(videoElems[0].videoHeight, 48,
+       "sink is same height as source, modulo our cropping algorithm");
+    is(videoElems[1].videoWidth, 24,
+       "sink is 1/2 width of source, modulo our cropping algorithm");
+    is(videoElems[1].videoHeight, 24,
+       "sink is 1/2 height of source, modulo our cropping algorithm");
+
+    emitter.stop();
+    videoStream.getVideoTracks()[0].stop();
+    offerer.close();
+    answerer.close();
   });
 </script>
 </pre>
diff --git a/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastOffer_lowResFirst.html b/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastOffer_lowResFirst.html
index efc487600bcd..182c6e67ff02 100644
--- a/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastOffer_lowResFirst.html
+++ b/dom/media/webrtc/tests/mochitests/test_peerConnection_simulcastOffer_lowResFirst.html
@@ -4,6 +4,8 @@
   <script type="application/javascript" src="pc.js"></script>
   <script type="application/javascript" src="parser_rtp.js"></script>
   <script type="application/javascript" src="/tests/dom/canvas/test/captureStream_common.js"></script>
+  <script type="application/javascript" src="helpers_from_wpt/sdp.js"></script>
+  <script type="application/javascript" src="simulcast.js"></script>
 </head>
 <body>
 <pre id="test">
@@ -14,172 +16,85 @@
     visible: true
   });
 
-  function addRIDExtension(pc, extensionId) {
-    const receivers = pc._pc.getReceivers();
-    is(receivers.length, 1, "We have exactly one RTP receiver");
-    const receiver = receivers[0];
-
-    SpecialPowers.wrap(receiver).mozAddRIDExtension(extensionId);
-  }
-
-  function selectRecvRID(pc, rid) {
-    const receivers = pc._pc.getReceivers();
-    is(receivers.length, 1, "We have exactly one RTP receiver");
-    const receiver = receivers[0];
-
-    SpecialPowers.wrap(receiver).mozAddRIDFilter(rid);
-  }
-
   runNetworkTest(async () => {
     await pushPrefs(
-      ['media.peerconnection.simulcast', true],
-      // 180Kbps was determined empirically, set well-higher than
-      // the 80Kbps+overhead needed for the two simulcast streams.
-      // 100Kbps was apparently too low.
-      ['media.peerconnection.video.min_bitrate_estimate', 180*1000],
-    );
+        ['media.peerconnection.simulcast', true],
+        // 180Kbps was determined empirically, set well-higher than
+        // the 80Kbps+overhead needed for the two simulcast streams.
+        // 100Kbps was apparently too low.
+        ['media.peerconnection.video.min_bitrate_estimate', 180*1000]);
 
-    let emitter, helper;
 
-    const test = new PeerConnectionTest({bundle: false});
-    test.setMediaConstraints([{video: true}], []);
+    const offerer = new RTCPeerConnection();
+    const answerer = new RTCPeerConnection();
 
-    test.chain.replace("PC_LOCAL_GUM", [
-      function PC_LOCAL_CANVAS_CAPTURESTREAM(test) {
-        emitter = new VideoFrameEmitter();
-        helper = new VideoStreamHelper();
-        test.pcLocal.attachLocalStream(emitter.stream());
-        emitter.start();
-      }
-    ]);
+    const add = (pc, can, failed) => can && pc.addIceCandidate(can).catch(failed);
+    offerer.onicecandidate = e => add(answerer, e.candidate, generateErrorCallback());
+    answerer.onicecandidate = e => add(offerer, e.candidate, generateErrorCallback());
 
-    test.chain.insertBefore('PC_LOCAL_CREATE_OFFER', [
-      function PC_LOCAL_SET_RIDS(test) {
-        const senders = test.pcLocal._pc.getSenders();
-        is(senders.length, 1, "We have exactly one RTP sender");
-        const sender = senders[0];
-        ok(sender.track, "Sender has a track");
+    const metadataToBeLoaded = [];
+    answerer.ontrack = (e) => {
+      metadataToBeLoaded.push(getPlaybackWithLoadedMetadata(e.track));
+    };
 
-        return sender.setParameters({
-          encodings: [{ rid: "foo", maxBitrate: 40000, scaleResolutionDownBy: 2 },
-                      { rid: "bar", maxBitrate: 40000 }]
-        });
-      }
-    ]);
+    // One send transceiver, that will be used to send both simulcast streams
+    const emitter = new VideoFrameEmitter();
+    const videoStream = emitter.stream();
+    offerer.addTrack(videoStream.getVideoTracks()[0], videoStream);
+    emitter.start();
 
-    test.chain.insertAfter('PC_LOCAL_GET_ANSWER', [
-      function PC_LOCAL_ADD_RIDS_TO_ANSWER(test) {
-        test._remote_answer.sdp = sdputils.transferSimulcastProperties(
-          test.originalOffer.sdp, test._remote_answer.sdp);
-        info("Answer with RIDs: " + JSON.stringify(test._remote_answer));
-        ok(test._remote_answer.sdp.match(/a=simulcast:/), "Modified answer has simulcast");
-        ok(test._remote_answer.sdp.match(/a=rid:foo/), "Modified answer has rid foo");
-        ok(test._remote_answer.sdp.match(/a=rid:bar/), "Modified answer has rid bar");
-        ok(test._remote_answer.sdp.match(/urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id/), "Modified answer has RID");
-      }
-    ]);
+    const sender = offerer.getSenders()[0];
+    sender.setParameters({
+        encodings: [
+            { rid: '0', maxBitrate: 40000, scaleResolutionDownBy: 2 },
+            { rid: '1', maxBitrate: 40000 }
+          ]
+    });
 
-    // For storing the rid extension so it can be checked in the RTP
-    let ridExtensionId = 0;
+    const offer = await offerer.createOffer();
 
-    // do this after set local description so the MediaPipeline
-    // has been created.
-    test.chain.insertAfter('PC_REMOTE_SET_LOCAL_DESCRIPTION',[
-      function PC_REMOTE_SET_RTP_FIRST_RID(test) {
-        const extmap_id = test.originalOffer.sdp.match(
-            "a=extmap:([0-9+])/sendonly urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id");
-        ok(extmap_id, "Original offer has extmap id for simulcast: " + extmap_id[1]);
-        ridExtensionId = extmap_id[1];
-        // Cause pcRemote to filter out everything but RID "foo", only
-        // allowing one of the simulcast streams through.
-        addRIDExtension(test.pcRemote, extmap_id[1]);
-        selectRecvRID(test.pcRemote, "foo");
-      }
-    ]);
+    const mungedOffer = ridToMid(offer.sdp);
+    info(`Transformed send simulcast offer to multiple m-sections: ${offer.sdp} to ${mungedOffer}`);
 
-    let getRtpPacket = (pc) => {
-      pc.mozEnablePacketDump(0, "rtp", false);
-      return new Promise((res, rej) =>
-        pc.mozSetPacketCallback((...args) => {
-          res([...args]);
-          pc.mozSetPacketCallback(() => {});
-          pc.mozDisablePacketDump(0, "rtp", false);
-        })
-      );
-    }
+    await answerer.setRemoteDescription({type: 'offer', sdp: mungedOffer});
+    await offerer.setLocalDescription(offer);
 
-    test.chain.insertBefore('PC_REMOTE_WAIT_FOR_MEDIA_FLOW', [
-        async function PC_REMOTE_CHECK_RID_IN_RTP() {
-          let pc = SpecialPowers.wrap(test.pcRemote._pc);
-          let [level, type, sending, data] =  await getRtpPacket(pc);
-          let extensions = ParseRtpPacket(data).header.extensions;
-          ok(ridExtensionId, "RID extension ID has been extracted from SDP");
-          let ridExt = extensions.find(e => e.id == ridExtensionId);
-          ok(ridExt, "RID is present in RTP.");
-          is(new TextDecoder('utf-8').decode(ridExt.data), "foo",
-             "RID is 'foo'.");
-        }
-    ]);
+    const rids = answerer.getTransceivers().map(t => t.mid);
+    is(rids.length, 2, 'Should have 2 mids in offer');
+    ok(rids[0] != '', 'First mid should be non-empty');
+    ok(rids[1] != '', 'Second mid should be non-empty');
+    info(`rids: ${JSON.stringify(rids)}`);
 
-    test.chain.append([
-      async function PC_REMOTE_WAIT_FOR_FRAMES() {
-        const vremote = test.pcRemote.remoteMediaElements[0];
-        ok(vremote, "Should have remote video element for pcRemote");
-        emitter.start();
-        await helper.checkVideoPlaying(vremote);
-        emitter.stop();
-      },
-      function PC_REMOTE_CHECK_SIZE_1() {
-        const vlocal = test.pcLocal.localMediaElements[0];
-        const vremote = test.pcRemote.remoteMediaElements[0];
-        ok(vlocal, "Should have local video element for pcLocal");
-        ok(vremote, "Should have remote video element for pcRemote");
-        is(vlocal.videoWidth, 50, "correct source width");
-        is(vlocal.videoHeight, 50, "correct source height");
-        is(vremote.videoWidth, 24,
-           "sink is 1/2 width of source, modulo our cropping algorithm");
-        is(vremote.videoHeight, 24,
-           "sink is 1/2 height of source, modulo our cropping algorithm");
-      },
-      function PC_REMOTE_SET_RTP_SECOND_RID(test) {
-        // Now, cause pcRemote to filter out everything but RID "bar", only
-        // allowing the other simulcast stream through.
-        selectRecvRID(test.pcRemote, "bar");
-      },
-      function PC_REMOTE_WAIT_FOR_SECOND_MEDIA_FLOW(test) {
-        return test.pcRemote.waitForMediaFlow();
-      },
-      async function PC_REMOTE_WAIT_FOR_FRAMES_2() {
-        const vremote = test.pcRemote.remoteMediaElements[0];
-        ok(vremote, "Should have remote video element for pcRemote");
-        emitter.start();
-        await helper.checkVideoPlaying(vremote);
-        emitter.stop();
-      },
-      // For some reason, even though we're getting a 25x25 stream, sometimes
-      // the resolution isn't updated on the video element on the first frame.
-      async function PC_REMOTE_WAIT_FOR_FRAMES_3() {
-        const vremote = test.pcRemote.remoteMediaElements[0];
-        ok(vremote, "Should have remote video element for pcRemote");
-        emitter.start();
-        await helper.checkVideoPlaying(vremote);
-        emitter.stop();
-      },
-      function PC_REMOTE_CHECK_SIZE_2() {
-        const vlocal = test.pcLocal.localMediaElements[0];
-        const vremote = test.pcRemote.remoteMediaElements[0];
-        ok(vlocal, "Should have local video element for pcLocal");
-        ok(vremote, "Should have remote video element for pcRemote");
-        is(vlocal.videoWidth, 50, "correct source width");
-        is(vlocal.videoHeight, 50, "correct source height");
-        is(vremote.videoWidth, 48,
-           "sink is same width as source, modulo our cropping algorithm");
-        is(vremote.videoHeight, 48,
-           "sink is same height as source, modulo our cropping algorithm");
-      },
-    ]);
+    const answer = await answerer.createAnswer();
 
-    await test.run();
+    const mungedAnswer = midToRid(answer.sdp);
+    info(`Transformed recv answer to simulcast: ${answer.sdp} to ${mungedAnswer}`);
+    await offerer.setRemoteDescription({type: 'answer', sdp: mungedAnswer});
+    await answerer.setLocalDescription(answer);
+
+    is(metadataToBeLoaded.length, 2, 'Offerer should have gotten 2 ontrack events');
+    info('Waiting for 2 loadedmetadata events');
+    const videoElems = await Promise.all(metadataToBeLoaded);
+
+    const helper = new VideoStreamHelper();
+    info('Waiting for first video element to start playing');
+    await helper.checkVideoPlaying(videoElems[0]);
+    info('Waiting for second video element to start playing');
+    await helper.checkVideoPlaying(videoElems[1]);
+
+    is(videoElems[1].videoWidth, 48,
+       "sink is same width as source, modulo our cropping algorithm");
+    is(videoElems[1].videoHeight, 48,
+       "sink is same height as source, modulo our cropping algorithm");
+    is(videoElems[0].videoWidth, 24,
+       "sink is 1/2 width of source, modulo our cropping algorithm");
+    is(videoElems[0].videoHeight, 24,
+       "sink is 1/2 height of source, modulo our cropping algorithm");
+
+    emitter.stop();
+    videoStream.getVideoTracks()[0].stop();
+    offerer.close();
+    answerer.close();
   });
 </script>
 </pre>
diff --git a/dom/media/webrtc/transportbridge/MediaPipeline.cpp b/dom/media/webrtc/transportbridge/MediaPipeline.cpp
index ab93db7fe22e..ccb377217097 100644
--- a/dom/media/webrtc/transportbridge/MediaPipeline.cpp
+++ b/dom/media/webrtc/transportbridge/MediaPipeline.cpp
@@ -353,31 +353,6 @@ void MediaPipeline::UpdateTransport_s(
   }
 }
 
-void MediaPipeline::AddRIDExtension_m(size_t aExtensionId) {
-  RUN_ON_THREAD(mStsThread,
-                WrapRunnable(RefPtr<MediaPipeline>(this),
-                             &MediaPipeline::AddRIDExtension_s, aExtensionId),
-                NS_DISPATCH_NORMAL);
-}
-
-void MediaPipeline::AddRIDExtension_s(size_t aExtensionId) {
-  mRtpParser->RegisterRtpHeaderExtension(webrtc::kRtpExtensionRtpStreamId,
-                                         aExtensionId);
-}
-
-void MediaPipeline::AddRIDFilter_m(const std::string& aRid) {
-  RUN_ON_THREAD(mStsThread,
-                WrapRunnable(RefPtr<MediaPipeline>(this),
-                             &MediaPipeline::AddRIDFilter_s, aRid),
-                NS_DISPATCH_NORMAL);
-}
-
-void MediaPipeline::AddRIDFilter_s(const std::string& aRid) {
-  // Running a simulcast test, ignore other filtering
-  mFilter = MakeUnique<MediaPipelineFilter>();
-  mFilter->AddRemoteRtpStreamId(aRid);
-}
-
 void MediaPipeline::GetContributingSourceStats(
     const nsString& aInboundRtpStreamId,
     FallibleTArray<dom::RTCRTPContributingSourceStats>& aArr) const {
diff --git a/dom/media/webrtc/transportbridge/MediaPipeline.h b/dom/media/webrtc/transportbridge/MediaPipeline.h
index e39882e1c521..cbffb6ff8a2d 100644
--- a/dom/media/webrtc/transportbridge/MediaPipeline.h
+++ b/dom/media/webrtc/transportbridge/MediaPipeline.h
@@ -103,15 +103,6 @@ class MediaPipeline : public sigslot::has_slots<> {
   void UpdateTransport_s(const std::string& aTransportId,
                          UniquePtr<MediaPipelineFilter>&& aFilter);
 
-  // Used only for testing; adds RTP header extension for RTP Stream Id with
-  // the given id.
-  void AddRIDExtension_m(size_t aExtensionId);
-  void AddRIDExtension_s(size_t aExtensionId);
-  // Used only for testing; installs a MediaPipelineFilter that filters
-  // everything but the given RID
-  void AddRIDFilter_m(const std::string& aRid);
-  void AddRIDFilter_s(const std::string& aRid);
-
   virtual DirectionType Direction() const { return mDirection; }
   size_t Level() const { return mLevel; }
   virtual bool IsVideo() const = 0;
diff --git a/dom/media/webrtc/transportbridge/MediaPipelineFilter.cpp b/dom/media/webrtc/transportbridge/MediaPipelineFilter.cpp
index e0c184b7f236..c791f0ef09e0 100644
--- a/dom/media/webrtc/transportbridge/MediaPipelineFilter.cpp
+++ b/dom/media/webrtc/transportbridge/MediaPipelineFilter.cpp
@@ -33,21 +33,6 @@ void MediaPipelineFilter::SetRemoteMediaStreamId(
   }
 }
 
-void MediaPipelineFilter::AddRtpExtensionMapping(
-    const webrtc::RtpExtension& aExt) {
-  mExtMap.push_back(aExt);
-}
-
-Maybe<webrtc::RtpExtension> MediaPipelineFilter::GetRtpExtension(
-    const std::string& aUri) const {
-  for (const auto& ext : mExtMap) {
-    if (ext.uri == aUri) {
-      return Some(ext);
-    }
-  }
-  return Nothing();
-}
-
 bool MediaPipelineFilter::Filter(const webrtc::RTPHeader& header) {
   DEBUG_LOG(("MediaPipelineFilter inspecting seq# %u SSRC: %u",
              header.sequenceNumber, header.ssrc));
@@ -97,17 +82,6 @@ bool MediaPipelineFilter::Filter(const webrtc::RTPHeader& header) {
   // RTP-STREAM-ID based filtering (for tests only)
   //
 
-  const auto streamId = fromStreamId(header.extension.stream_id);
-  if (streamId && !remote_rid_set_.empty()) {
-    if (remote_rid_set_.count(streamId.value())) {
-      DEBUG_LOG(("MediaPipelineFilter RID: %s matched. passing packet",
-                 streamId.value().c_str()));
-      return true;
-    }
-    DEBUG_LOG(("MediaPipelineFilter RID: %s did not match any of %zu RIDs",
-               streamId.value().c_str(), remote_rid_set_.size()));
-  }
-
   //
   // Remote SSRC based filtering
   //
@@ -152,10 +126,6 @@ void MediaPipelineFilter::AddRemoteSSRC(uint32_t ssrc) {
   remote_ssrc_set_.insert(ssrc);
 }
 
-void MediaPipelineFilter::AddRemoteRtpStreamId(const std::string& rtp_strm_id) {
-  remote_rid_set_.insert(rtp_strm_id);
-}
-
 void MediaPipelineFilter::AddUniquePT(uint8_t payload_type) {
   payload_type_set_.insert(payload_type);
 }
diff --git a/dom/media/webrtc/transportbridge/MediaPipelineFilter.h b/dom/media/webrtc/transportbridge/MediaPipelineFilter.h
index f414e750e6a3..9b40bceda8a6 100644
--- a/dom/media/webrtc/transportbridge/MediaPipelineFilter.h
+++ b/dom/media/webrtc/transportbridge/MediaPipelineFilter.h
@@ -62,9 +62,6 @@ class MediaPipelineFilter {
   bool Filter(const webrtc::RTPHeader& header);
 
   void AddRemoteSSRC(uint32_t ssrc);
-  void AddRemoteRtpStreamId(const std::string& rtp_strm_id);
-  // Used to set Extention Mappings for tests
-  void AddRtpExtensionMapping(const webrtc::RtpExtension& aExt);
 
   void SetRemoteMediaStreamId(const Maybe<std::string>& aMid);
 
@@ -76,13 +73,10 @@ class MediaPipelineFilter {
   std::vector<webrtc::RtpExtension> GetExtmap() const { return mExtMap; }
 
  private:
-  Maybe<webrtc::RtpExtension> GetRtpExtension(const std::string& aUri) const;
   // The number of filters we manage here is quite small, so I am optimizing
   // for readability.
   std::set<uint32_t> remote_ssrc_set_;
   std::set<uint8_t> payload_type_set_;
-  // Set by tests, sticky
-  std::set<std::string> remote_rid_set_;
   Maybe<std::string> mRemoteMid;
   std::set<uint32_t> mRemoteMidBindings;
   // RID extension can be set by tests and is sticky, the rest of
diff --git a/dom/webidl/RTCRtpReceiver.webidl b/dom/webidl/RTCRtpReceiver.webidl
index 16b14e908a3c..72691dbc4d67 100644
--- a/dom/webidl/RTCRtpReceiver.webidl
+++ b/dom/webidl/RTCRtpReceiver.webidl
@@ -18,10 +18,6 @@ interface RTCRtpReceiver {
   [Pref="media.peerconnection.rtpsourcesapi.enabled"]
   sequence<RTCRtpSynchronizationSource> getSynchronizationSources();
 
-  [ChromeOnly]
-  void mozAddRIDExtension(unsigned short extensionId);
-  [ChromeOnly]
-  void mozAddRIDFilter(DOMString rid);
   // test-only: for testing getContributingSources
   [ChromeOnly]
   void mozInsertAudioLevelForContributingSource(unsigned long source,