diff --git a/dom/tests/mochitest/bugs/Makefile.in b/dom/tests/mochitest/bugs/Makefile.in
index 012ee5e9f3b..6145bf55b23 100644
--- a/dom/tests/mochitest/bugs/Makefile.in
+++ b/dom/tests/mochitest/bugs/Makefile.in
@@ -137,6 +137,7 @@ MOCHITEST_FILES	= \
 		test_sizetocontent_clamp.html \
 		test_protochains.html \
 		test_bug817476.html \
+		test_bug823173.html \
 		$(NULL)
 
 ifneq (Linux,$(OS_ARCH))
diff --git a/dom/tests/mochitest/bugs/test_bug823173.html b/dom/tests/mochitest/bugs/test_bug823173.html
new file mode 100644
index 00000000000..15748786c66
--- /dev/null
+++ b/dom/tests/mochitest/bugs/test_bug823173.html
@@ -0,0 +1,30 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=823173
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 823173</title>
+  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=823173">Mozilla Bug 823173</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+  
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 823173 **/
+try {
+  ok(!(navigator instanceof Window), "navigator is not an instance of Window");
+} catch (e) {
+  ok(false, "instanceof tests should not throw");
+}
+</script>
+</pre>
+</body>
+</html>
