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diff --git a/layout/base/tests/test_bug851485.html b/layout/base/tests/test_bug851485.html
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+++ b/layout/base/tests/test_bug851485.html
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+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=851485
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 851485</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script src="/tests/SimpleTest/EventUtils.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 851485 **/
+
+SimpleTest.waitForExplicitFinish();
+
+var testRunning = false;
+async function runTest() {
+  if (testRunning) {
+    return;
+  }
+  testRunning = true;
+
+  var e = document.getElementsByTagName('iframe')[0];
+  var win = e.contentWindow;
+
+  var p = new Promise((r) => { win.addEventListener("hashchange", r, { once: true }); });
+  win.location.hash = '#anchor';
+  await p;
+
+  win.scrollTo(0, 500);
+
+  p = new Promise((r) => { e.addEventListener("load", r, { once: true }); });
+  win.location.reload();
+  await p;
+
+  is(win.location.hash, "#anchor", "We set the location's hash to 'anchor'");
+  // Allow a half pixel difference because the scroll position is aligned with
+  // screen pixels instead of CSS pixels (bug 1774315).
+  isfuzzy(win.scrollY, 500, 0.5, "Reloading keeps scroll position");
+
+  var link = win.document.getElementsByTagName('a')[0];
+  var anchor = win.document.getElementsByTagName('a')[1];
+  p = new Promise((r) => {
+    var observer = new IntersectionObserver((entries) => {
+      info("IntersectionObserver: entering callback")
+      if (entries.some((entry) => entry.isIntersecting)) {
+        info("IntersectionObserver: some entry isIntersecting; disconnecting")
+        observer.disconnect();
+        r();
+      }
+    });
+    observer.observe(anchor);
+  });
+  win.document.body.offsetHeight;
+  synthesizeMouseAtCenter(link, {type: "mousedown"}, win);
+  synthesizeMouseAtCenter(link, {type: "mouseup"}, win);
+  info("Sending click")
+  sendMouseEvent({type: "click"}, link, win);
+  await p;
+  let actualScroll = win.scrollY;
+  info("Promise resolved (for IntersectionObserver). win.scrollY is " +
+       actualScroll);
+
+  ok(actualScroll > 3000, "Scrolling after load works.");
+
+  SimpleTest.finish();
+}
+
+
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=851485">Mozilla Bug 851485</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+</div>
+<pre id="test">
+</pre>
+<iframe src="file_bug842853.html"></iframe>
+<script>
+
+</script>
+</body>
+</html>