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diff --git a/gfx/layers/apz/test/mochitest/helper_scroll_snap_resnap_after_async_scrollBy.html b/gfx/layers/apz/test/mochitest/helper_scroll_snap_resnap_after_async_scrollBy.html
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+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1">
+  <title>Re-snapping to the last snapped element on APZ</title>
+  <script src="apz_test_utils.js"></script>
+  <script src="apz_test_native_event_utils.js"></script>
+  <script src="/tests/SimpleTest/paint_listener.js"></script>
+  <style>
+    body {
+      margin: 0;
+    }
+    div {
+      position: absolute;
+    }
+    #scroller {
+      width: 100%;
+      height: 500px;
+      overflow-y: scroll;
+      scroll-snap-type: y proximity; /* to escape from the last snap point */
+    }
+    .child {
+      width: 100%;
+      height: 100px;
+      background-color: blue;
+      scroll-snap-align: start;
+    }
+  </style>
+</head>
+<body>
+  <div id="scroller">
+    <div class="child" style="top: 0px;"></div>
+    <div class="child" style="top: 200px;"></div>
+    <div id="spacer" style="width: 100%; height: 2000px;"></div>
+  </div>
+  <script type="application/javascript">
+    async function test() {
+      const proximityThreshold = scroller.getBoundingClientRect().height * 0.3;
+
+      let transformEndPromise = promiseTransformEnd();
+      scroller.scrollBy({left: 0, top: 100, behavior: "smooth"});
+
+      await transformEndPromise;
+      await promiseApzFlushedRepaints();
+
+      is(scroller.scrollTop, 200, "snap to 200px");
+
+      document.querySelectorAll(".child")[1].style.top = "400px";
+      is(scroller.scrollTop, 400, "re-snap to 400px");
+
+      // Now trigger another async scroll to escape from the last snap point.
+      transformEndPromise = promiseTransformEnd();
+      scroller.scrollBy({left: 0, top: proximityThreshold + 100,
+                         behavior: "smooth"});
+
+      // Expand the scrollable region during the async scroll.
+      spacer.style.height = "2200px";
+
+      await transformEndPromise;
+      await promiseApzFlushedRepaints();
+
+      isnot(scroller.scrollTop, 400, "Do not re-snap to the original 400px point");
+    }
+
+    waitUntilApzStable()
+    .then(test)
+    .then(subtestDone, subtestFailed);
+  </script>
+</body>
+</html>