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diff --git a/gfx/layers/apz/test/mochitest/helper_fission_inactivescroller_under_oopif.html b/gfx/layers/apz/test/mochitest/helper_fission_inactivescroller_under_oopif.html
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+++ b/gfx/layers/apz/test/mochitest/helper_fission_inactivescroller_under_oopif.html
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+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Ensure inactive scollframes under OOPIFs hit-test properly</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script src="/tests/SimpleTest/paint_listener.js"></script>
+  <script src="helper_fission_utils.js"></script>
+  <script src="apz_test_utils.js"></script>
+  <script src="apz_test_native_event_utils.js"></script>
+  <script>
+
+fission_subtest_init();
+
+FissionTestHelper.startTestPromise
+  .then(waitUntilApzStable)
+  .then(loadOOPIFrame("testframe", "helper_fission_empty.html"))
+  .then(waitUntilApzStable)
+  .then(test)
+  .then(FissionTestHelper.subtestDone, FissionTestHelper.subtestFailed);
+
+let make_oopif_scrollable = function() {
+  // ensure the oopif is scrollable, and wait for the paint so that the
+  // compositor also knows it's scrollable.
+  document.body.style.height = "200vh";
+  promiseApzFlushedRepaints().then(() => {
+    let utils = SpecialPowers.getDOMWindowUtils(window);
+    let result = {
+      layersId: utils.getLayersId(),
+      viewId: utils.getViewId(document.scrollingElement)
+    };
+    dump(`OOPIF computed IDs ${JSON.stringify(result)}\n`);
+    FissionTestHelper.fireEventInEmbedder("OOPIF:Scrollable", result);
+  });
+  return true;
+};
+
+async function test() {
+  let iframe = document.getElementById("testframe");
+
+  let letScrollerIdPromise = promiseOneEvent(window, "OOPIF:Scrollable", null);
+  ok(await FissionTestHelper.sendToOopif(iframe, `(${make_oopif_scrollable})()`),
+     "Ran code to make OOPIF scrollable");
+  let oopifScrollerIds = (await letScrollerIdPromise).data;
+
+  // The #scroller div is (a) inactive, and (b) under the OOPIF. Hit-testing
+  // against it should hit the OOPIF.
+
+  checkHitResult(await fissionHitTest(centerOf("scroller"), iframe),
+                 APZHitResultFlags.VISIBLE,
+                 oopifScrollerIds.viewId,
+                 oopifScrollerIds.layersId,
+                 "Part of OOPIF sitting on top of the inactive scrollframe should hit OOPIF");
+}
+
+  </script>
+</head>
+<body>
+<style>
+html, body {
+    margin: 0;
+}
+body {
+    /* Ensure root document is scrollable so that #scroller is inactive by
+      default */
+    height: 200vh;
+}
+iframe {
+    position: fixed;
+    top: 0;
+    left: 0;
+    width: 300px;
+    height: 200px;
+}
+
+#scroller {
+    width: 200px;
+    height: 200px;
+    background-color: transparent;
+    overflow-y: scroll;
+}
+</style>
+<div id="scroller">
+  <div style="height:500px">inside scroller</div>
+</div>
+<iframe id="testframe"></iframe>
+</body>
+</html>