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diff --git a/layout/base/tests/test_bug469170.html b/layout/base/tests/test_bug469170.html
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+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=469170
+-->
+<head>
+  <title>Test for Bug 469170</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body onload="runTest();">
+<p><a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=469170">Mozilla Bug 469170</a></p>
+
+<iframe id="source" width="50" height="50" srcdoc="<html></html>"></iframe>
+
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 469170 **/
+
+SimpleTest.waitForExplicitFinish();
+
+function runTest() {
+  var source = document.getElementById('source').contentWindow;
+  rect = { left: 0, top: 0,
+           width: source.innerWidth, height: source.innerHeight };
+  var canvas = SpecialPowers.snapshotRect(source, rect, "transparent");
+  var context = canvas.getContext("2d");
+
+  var components = [ "red", "green", "blue", "alpha" ];
+
+  var data = context.getImageData(0, 0, canvas.width, canvas.height).data;
+  var failed = false;
+  for (var i = 0; i < data.length; i++) {
+    if (data[i] != 0) {
+      is(data[i], 0, "pixel " + Math.floor(i/4) + " " + components[i%4]);
+      failed = true;
+    }
+  }
+  if (!failed) {
+    ok(!failed, "all pixels fully transparent");
+  }
+  SimpleTest.finish();
+}
+</script>
+</pre>
+</body>
+</html>