diff --git a/dom/media/mediasource/test/init-trackid2.mp4 b/dom/media/mediasource/test/init-trackid2.mp4
new file mode 100644
index 000000000000..c96da9d4df17
Binary files /dev/null and b/dom/media/mediasource/test/init-trackid2.mp4 differ
diff --git a/dom/media/mediasource/test/init-trackid2.mp4^headers^ b/dom/media/mediasource/test/init-trackid2.mp4^headers^
new file mode 100644
index 000000000000..4030ea1d3ddb
--- /dev/null
+++ b/dom/media/mediasource/test/init-trackid2.mp4^headers^
@@ -0,0 +1 @@
+Cache-Control: no-store
diff --git a/dom/media/mediasource/test/init-trackid3.mp4 b/dom/media/mediasource/test/init-trackid3.mp4
new file mode 100644
index 000000000000..e37d8ea098b8
Binary files /dev/null and b/dom/media/mediasource/test/init-trackid3.mp4 differ
diff --git a/dom/media/mediasource/test/init-trackid3.mp4^headers^ b/dom/media/mediasource/test/init-trackid3.mp4^headers^
new file mode 100644
index 000000000000..4030ea1d3ddb
--- /dev/null
+++ b/dom/media/mediasource/test/init-trackid3.mp4^headers^
@@ -0,0 +1 @@
+Cache-Control: no-store
diff --git a/dom/media/mediasource/test/mochitest.ini b/dom/media/mediasource/test/mochitest.ini
index 9cd0cdf74ea9..3f8dce2651ba 100644
--- a/dom/media/mediasource/test/mochitest.ini
+++ b/dom/media/mediasource/test/mochitest.ini
@@ -49,6 +49,8 @@ support-files =
   tags_before_cluster.webm
   tags_before_cluster.webm^header^
   1516754.webm 1516754.webm^headers^
+  init-trackid2.mp4 init-trackid3.mp4 segment-2.0001.m4s segment-2.0001.m4s segment-3.0001.m4s segment-3.0002.m4s
+  init-trackid2.mp4^headers^ init-trackid3.mp4^headers^ segment-2.0001.m4s^headers^ segment-2.0001.m4s^headers^ segment-3.0001.m4s^headers^ segment-3.0002.m4s^headers^
 
 [test_AbortAfterPartialMediaSegment.html]
 [test_AppendPartialInitSegment.html]
@@ -143,6 +145,7 @@ skip-if = toolkit == 'android' # Not supported on android
 skip-if = toolkit == 'android' # Not supported on android
 [test_TimestampOffset_mp4.html]
 skip-if = toolkit == 'android' # Not supported on android
+[test_trackidchange_mp4.html]
 [test_TruncatedDuration.html]
 [test_TruncatedDuration_mp4.html]
 skip-if = toolkit == 'android' # Not supported on android
diff --git a/dom/media/mediasource/test/segment-2.0001.m4s b/dom/media/mediasource/test/segment-2.0001.m4s
new file mode 100644
index 000000000000..b63fd6aaa6c4
Binary files /dev/null and b/dom/media/mediasource/test/segment-2.0001.m4s differ
diff --git a/dom/media/mediasource/test/segment-2.0001.m4s^headers^ b/dom/media/mediasource/test/segment-2.0001.m4s^headers^
new file mode 100644
index 000000000000..4030ea1d3ddb
--- /dev/null
+++ b/dom/media/mediasource/test/segment-2.0001.m4s^headers^
@@ -0,0 +1 @@
+Cache-Control: no-store
diff --git a/dom/media/mediasource/test/segment-2.0002.m4s b/dom/media/mediasource/test/segment-2.0002.m4s
new file mode 100644
index 000000000000..3a0051f10e81
Binary files /dev/null and b/dom/media/mediasource/test/segment-2.0002.m4s differ
diff --git a/dom/media/mediasource/test/segment-2.0002.m4s^headers^ b/dom/media/mediasource/test/segment-2.0002.m4s^headers^
new file mode 100644
index 000000000000..4030ea1d3ddb
--- /dev/null
+++ b/dom/media/mediasource/test/segment-2.0002.m4s^headers^
@@ -0,0 +1 @@
+Cache-Control: no-store
diff --git a/dom/media/mediasource/test/segment-3.0001.m4s b/dom/media/mediasource/test/segment-3.0001.m4s
new file mode 100644
index 000000000000..71e33f0e8f9f
Binary files /dev/null and b/dom/media/mediasource/test/segment-3.0001.m4s differ
diff --git a/dom/media/mediasource/test/segment-3.0001.m4s^headers^ b/dom/media/mediasource/test/segment-3.0001.m4s^headers^
new file mode 100644
index 000000000000..4030ea1d3ddb
--- /dev/null
+++ b/dom/media/mediasource/test/segment-3.0001.m4s^headers^
@@ -0,0 +1 @@
+Cache-Control: no-store
diff --git a/dom/media/mediasource/test/segment-3.0002.m4s b/dom/media/mediasource/test/segment-3.0002.m4s
new file mode 100644
index 000000000000..10a3ce695d56
Binary files /dev/null and b/dom/media/mediasource/test/segment-3.0002.m4s differ
diff --git a/dom/media/mediasource/test/segment-3.0002.m4s^headers^ b/dom/media/mediasource/test/segment-3.0002.m4s^headers^
new file mode 100644
index 000000000000..4030ea1d3ddb
--- /dev/null
+++ b/dom/media/mediasource/test/segment-3.0002.m4s^headers^
@@ -0,0 +1 @@
+Cache-Control: no-store
diff --git a/dom/media/mediasource/test/test_trackidchange_mp4.html b/dom/media/mediasource/test/test_trackidchange_mp4.html
new file mode 100644
index 000000000000..fdbeece3cd2e
--- /dev/null
+++ b/dom/media/mediasource/test/test_trackidchange_mp4.html
@@ -0,0 +1,32 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>MSE: test append of audio with similar init segments that have different track ids</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="text/javascript" src="mediasource.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+SimpleTest.waitForExplicitFinish();
+
+runWithMSE(async (ms, el) => {
+  el.controls = true;
+  await once(ms, "sourceopen");
+  ok(true, "Receive a sourceopen event");
+  const audiosb = ms.addSourceBuffer("audio/mp4");
+  await fetchAndLoad(audiosb, "init-trackid2", [''], ".mp4");
+  await fetchAndLoad(audiosb, "segment-2.0001", [''], ".m4s");
+  await fetchAndLoad(audiosb, "init-trackid3", [''], ".mp4");
+  await fetchAndLoad(audiosb, "segment-3.0002", [''], ".m4s");
+  is(el.buffered.length, 1, "data is buffered");
+  is(el.buffered.end(0), 8, "all data got appended");
+  SimpleTest.finish();
+});
+
+</script>
+</pre>
+</body>
+</html>