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diff --git a/layout/base/tests/browser_bug1701027-1.js b/layout/base/tests/browser_bug1701027-1.js
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+/* This test is based on
+     https://searchfox.org/mozilla-central/rev/e082df56bbfeaff0f388e7da9da401ff414df18f/gfx/layers/apz/test/mochitest/browser_test_select_zoom.js
+*/
+
+// In order for this test to test the original bug we need:
+// 1) At least e10s enabled so that apz is enabled so we can create an
+//    nsDisplayAsyncZoom item
+//    (the insertion of this item without marking the required frame modified
+//     is what causes the bug in the retained display list merging)
+// 2) a root content document, again so that we can create a nsDisplayAsyncZoom
+//    item
+// 3) the root content document cannot have a display port to start
+//    (if it has a display port then it gets a nsDisplayAsyncZoom, but we need
+//     that to be created after the anonymous content we insert into the
+//     document)
+// Point 3) requires the root content document to be in the parent process,
+// since if it is in a content process it will get a displayport for being at
+// the root of a process.
+// Creating an in-process root content document I think is not possible in
+// mochitest-plain. mochitest-chrome does not have e10s enabled. So this has to
+// be a mochitest-browser-chrome test.
+
+// Outline of this test:
+// Open a new tab with a pretty simple content file, that is not scrollable
+// Use the anonymous content api to insert into that content doc
+// Send a mouse click over the content doc
+// The click hits fixed pos content.
+// This sets a displayport on the root scroll frame of the content doc.
+// (This is because we call GetAsyncScrollableAncestorFrame in
+// PrepareForSetTargetAPZCNotification
+// https://searchfox.org/mozilla-central/rev/e082df56bbfeaff0f388e7da9da401ff414df18f/gfx/layers/apz/util/APZCCallbackHelper.cpp#624
+// which passes the SCROLLABLE_FIXEDPOS_FINDS_ROOT flag
+// https://searchfox.org/mozilla-central/rev/e082df56bbfeaff0f388e7da9da401ff414df18f/layout/base/nsLayoutUtils.cpp#2884
+// so starting from fixed pos content means we always find the root scroll
+// frame, whereas if we started from non-fixed content we'd walk pass the root
+// scroll frame becase it isn't scrollable.)
+// Then we have to be careful not to do anything that causes a full display
+// list rebuild.
+// And finally we change the color of the fixed element which covers the whole
+// viewport which causes us to do a partial display list update including the
+// anonymous content, which hits the assert we are aiming to test.
+
+add_task(async function () {
+  function getChromeURL(filename) {
+    let chromeURL = getRootDirectory(gTestPath) + filename;
+    return chromeURL;
+  }
+
+  // We need this otherwise there is a burst animation on the new tab when it
+  // loads and that somehow scrolls a scroll frame, which makes it active,
+  // which makes the scrolled frame an AGR, which means we have multiple AGRs
+  // (the display port makes the root scroll frame active and an AGR) so we hit
+  // this
+  // https://searchfox.org/mozilla-central/rev/e082df56bbfeaff0f388e7da9da401ff414df18f/layout/painting/RetainedDisplayListBuilder.cpp#1179
+  // and are forced to do a full display list rebuild and that prevents us from
+  // testing the original bug.
+  await SpecialPowers.pushPrefEnv({
+    set: [["ui.prefersReducedMotion", 1]],
+  });
+
+  const pageUrl = getChromeURL("helper_bug1701027-1.html");
+  let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, pageUrl);
+
+  const [theX, theY] = await SpecialPowers.spawn(
+    tab.linkedBrowser,
+    [],
+    async () => {
+      content.document.body.offsetWidth;
+
+      await new Promise(r => content.window.requestAnimationFrame(r));
+
+      const rect = content.document
+        .getElementById("fd")
+        .getBoundingClientRect();
+      const x = content.window.mozInnerScreenX + rect.left + rect.width / 2;
+      const y = content.window.mozInnerScreenY + rect.top + rect.height / 2;
+
+      let doc = SpecialPowers.wrap(content.document);
+      var bq = doc.createElement("blockquote");
+      bq.textContent = "This blockquote text.";
+      var div = doc.createElement("div");
+      div.textContent = " This div text.";
+      bq.appendChild(div);
+      var ac = doc.insertAnonymousContent(bq);
+      content.document.body.offsetWidth;
+
+      await new Promise(r => content.window.requestAnimationFrame(r));
+      await new Promise(r => content.window.requestAnimationFrame(r));
+
+      return [x, y];
+    }
+  );
+
+  EventUtils.synthesizeNativeMouseEvent({
+    type: "click",
+    target: window.document.documentElement,
+    screenX: theX,
+    screenY: theY,
+  });
+
+  await new Promise(resolve => setTimeout(resolve, 0));
+  await SpecialPowers.spawn(tab.linkedBrowser, [], async () => {
+    await new Promise(r => content.window.requestAnimationFrame(r));
+    await new Promise(r => content.window.requestAnimationFrame(r));
+  });
+
+  await SpecialPowers.spawn(tab.linkedBrowser, [], async () => {
+    content.document.getElementById("fd").style.backgroundColor = "blue";
+  });
+
+  await new Promise(resolve => setTimeout(resolve, 0));
+  await SpecialPowers.spawn(tab.linkedBrowser, [], async () => {
+    await new Promise(r => content.window.requestAnimationFrame(r));
+    await new Promise(r => content.window.requestAnimationFrame(r));
+  });
+
+  await SpecialPowers.spawn(tab.linkedBrowser, [], async () => {
+    content.document.getElementById("fd").style.backgroundColor = "red";
+  });
+
+  await new Promise(resolve => setTimeout(resolve, 0));
+  await SpecialPowers.spawn(tab.linkedBrowser, [], async () => {
+    await new Promise(r => content.window.requestAnimationFrame(r));
+    await new Promise(r => content.window.requestAnimationFrame(r));
+  });
+
+  BrowserTestUtils.removeTab(tab);
+
+  ok(true, "didn't crash");
+});