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diff --git a/layout/reftests/transform/partial-prerender-translate-8.html b/layout/reftests/transform/partial-prerender-translate-8.html
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+++ b/layout/reftests/transform/partial-prerender-translate-8.html
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+<!DOCTYPE html>
+<html class="reftest-wait reftest-no-flush">
+<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
+<!--
+  A test for a partial pre-rendered transform in an iframe, if the clip
+  rectangle of the transform animation were wrong, e.g. (800, 1000), the
+  transform animation janks at the initial position.
+  -->
+<style>
+html {
+  overflow: hidden;
+}
+body {
+  margin: 0px;
+  padding: 0px;
+}
+</style>
+              <!-- a half width of the view port -->
+<iframe style="width:400px; height:1000px; border: 0"
+        srcdoc="<!DOCTYPE HTML>
+                <html>
+                <style>
+                html {
+                  overflow: hidden;
+                  scrollbar-width: none;
+                }
+                html, body {
+                  margin: 0;
+                  padding: 0;
+                }
+                @keyframes anim {
+                  /* the partial prerender area is (1125, 1000), thus         */
+                  /* translateX(-725px) is the position where the right edge  */
+                  /* of the partial prerender is positioned at the right edge */
+                  /* of the clip rect (400, 1000).                            */
+                  to { transform: translateX(-725px); }
+                }
+                #target {
+                  width: 1600px;
+                  height: 1000px;
+                  transform: translateX(0px);
+                }
+                </style>
+                <div id='target'>
+                  <svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 1600 1000'>
+                    <rect fill='green' x='0'   width='800' height='1000'></rect>
+                    <rect fill='blue'  x='800' width='325' height='1000'></rect>
+                    <rect fill='red'   x='1125' width='675' height='1000'></rect>
+                  </svg>
+                </div>
+                <script>
+                window.addEventListener('message', () => {
+                  if (event.data == 'start') {
+                    target.style.animation = 'anim 100s 1s step-start';
+                    target.addEventListener('animationstart', () => {
+                      parent.postMessage('animationstart', '*');
+                    });
+                  }
+                });
+                </script></html>">
+</iframe>
+<script>
+document.addEventListener("MozReftestInvalidate", () => {
+  document.querySelector("iframe").contentWindow.postMessage("start", "*");
+}, { once: true });
+
+window.addEventListener("message", event => {
+  if (event.data == "animationstart") {
+    document.documentElement.classList.remove('reftest-wait');
+  }
+});
+</script>
+</html>