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diff --git a/dom/media/test/test_suspend_media_by_inactive_docshell.html b/dom/media/test/test_suspend_media_by_inactive_docshell.html
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+++ b/dom/media/test/test_suspend_media_by_inactive_docshell.html
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+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test suspending media by inactive docShell</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script src="manifest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<video id="testVideo" src="gizmo.mp4" loop></video>
+<script class="testbody" type="text/javascript">
+/**
+ * When calling `browser.suspendMediaWhenInactive`, it can set the docShell's
+ * corresponding flag that is used to suspend media when the docShell is
+ * inactive. This test is used to check if we can suspend/resume the media
+ * correctly when changing docShell's active state.
+ */
+async function startTest() {
+  const video = document.getElementById("testVideo");
+
+  info(`start video`);
+  await video.play();
+
+  info(`set docShell inactive which would suspend media`);
+  await setDocShellActive(false);
+
+  info(`set docShell active which would resume media`);
+  await setDocShellActive(true);
+
+  SimpleTest.finish();
+}
+
+SimpleTest.waitForExplicitFinish();
+SpecialPowers.pushPrefEnv(
+  {"set": [["media.testing-only-events", true]]}, startTest);
+
+/**
+ * The following are test helper functions.
+ */
+function mediaSuspendedStateShouldEqualTo(expected) {
+  const video = document.getElementById("testVideo");
+  const result = SpecialPowers.wrap(video).isSuspendedByInactiveDocOrDocShell;
+  is(result, expected, `media's suspended state is correct`);
+}
+
+function setDocShellActive(isActive) {
+  const win = SpecialPowers.wrap(window);
+  const docShell = win.docShell;
+  const browsingContext = win.browsingContext;
+  // This flag is used to prevent media from playing when docShell is inactive.
+  browsingContext.top.suspendMediaWhenInactive = true;
+  browsingContext.isActive = isActive;
+  // After updating `docshell.isActive`, it would suspend/resume media and we
+  // wait suspending/resuming finishing by listening to `MozMediaSuspendChanged`
+  return new Promise(r => {
+    docShell.chromeEventHandler.addEventListener("MozMediaSuspendChanged",
+      () => {
+        mediaSuspendedStateShouldEqualTo(!isActive);
+        r();
+      }, {once : true}
+    );
+  });
+}
+
+</script>
+</body>
+</html>