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diff --git a/dom/canvas/test/test_drawSnapshot_fixed.html b/dom/canvas/test/test_drawSnapshot_fixed.html
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+++ b/dom/canvas/test/test_drawSnapshot_fixed.html
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+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Test for drawSnapshot</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script src="/tests/SimpleTest/WindowSnapshot.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <style>
+    html {
+      height: 2000px;
+      overflow: hidden;
+    }
+    header {
+      position: fixed;
+      background: red;
+      display: block;
+      left: 0;
+      right: 0;
+      top: 0;
+      height: 200px;
+    }
+  </style>
+  <script type="application/javascript">
+  function make_canvas() {
+    var canvas = document.createElement("canvas");
+    canvas.setAttribute("height", 2000);
+    canvas.setAttribute("width", 500);
+    return canvas;
+  }
+
+  SimpleTest.waitForExplicitFinish();
+  window.addEventListener("load", runTests);
+  
+  window.scrollTo(0, 1000);
+
+  async function runTests(event) {
+    var testCanvas = make_canvas();
+    var testCx = testCanvas.getContext("2d");
+    var testWrapCx = SpecialPowers.wrap(testCx);
+
+    // Take a snapshot of the page while scrolled down, so that the fixed header will
+    // be visually in the middle of the root scroll frame, but should still be at the
+    // top of the snapshot (since snapshots with a rect are taken relative to the document).
+    var rect = new window.DOMRect(0, 0, 500, 2000);
+    let image = await SpecialPowers.snapshotContext(window, rect, "rgb(255, 255, 255)", true);
+    testWrapCx.drawImage(image, 0, 0);
+
+    var refCanvas = make_canvas();
+    var refCx = refCanvas.getContext("2d");
+
+    // Construct a reference image with an equivalent red square at the top.
+    refCx.fillStyle = "white";
+    refCx.fillRect(0, 0, 500, 2000);
+    refCx.fillStyle = "red";
+    refCx.fillRect(0, 0, 500, 200);
+
+    assertSnapshots(testCanvas, refCanvas, true, null, "position:fixed element with scrolling", "reference");
+
+    SimpleTest.finish();
+  }
+
+  </script>
+</head>
+<body>
+  <header></header>
+</body>
+</html>