--- a/dom/browser-element/mochitest/Makefile.in
+++ b/dom/browser-element/mochitest/Makefile.in
@@ -54,12 +54,21 @@ include $(topsrcdir)/config/rules.mk
 		test_browserElement_oop_PromptCheck.html \
 		test_browserElement_inproc_PromptCheck.html \
 		browserElement_PromptConfirm.js \
 		test_browserElement_oop_PromptConfirm.html \
 		test_browserElement_inproc_PromptConfirm.html \
 		browserElement_Close.js \
 		test_browserElement_oop_Close.html \
 		test_browserElement_inproc_Close.html \
+		browserElement_OpenWindow.js \
+		test_browserElement_oop_OpenWindow.html \
+		test_browserElement_inproc_OpenWindow.html \
+		file_browserElement_Open1.html \
+		file_browserElement_Open2.html \
+		browserElement_OpenWindowRejected.js \
+		test_browserElement_oop_OpenWindowRejected.html \
+		test_browserElement_inproc_OpenWindowRejected.html \
+		file_browserElement_OpenWindowRejected.html \
 		$(NULL)
 
 libs:: $(_TEST_FILES)
 	$(INSTALL) $(foreach f,$^,"$f") $(DEPTH)/_tests/testing/mochitest/tests/$(relativesrcdir)

new file mode 100644
--- /dev/null
+++ b/dom/browser-element/mochitest/browserElement_OpenWindow.js
@@ -0,0 +1,59 @@
+/* Any copyright is dedicated to the public domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// Bug 742944 - Test that window.open works with <iframe mozbrowser>.
+
+"use strict";
+SimpleTest.waitForExplicitFinish();
+
+function runTest() {
+  browserElementTestHelpers.setEnabledPref(true);
+  browserElementTestHelpers.addToWhitelist();
+
+  var iframe = document.createElement('iframe');
+  iframe.mozbrowser = true;
+
+  var gotPopup = false;
+  iframe.addEventListener('mozbrowseropenwindow', function(e) {
+    is(gotPopup, false, 'Should get just one popup.');
+    gotPopup = true;
+
+    document.body.appendChild(e.detail.frameElement);
+
+    ok(/file_browserElement_Open2\.html$/.test(e.detail.url),
+       "Popup's URL (got " + e.detail.url + ")");
+    is(e.detail.name, "name");
+    is(e.detail.features, "features");
+  });
+
+  iframe.addEventListener('mozbrowsershowmodalprompt', function(e) {
+    ok(gotPopup, 'Got mozbrowseropenwindow event before showmodalprompt event.');
+    if (e.detail.message.indexOf("success:") == 0) {
+      ok(true, e.detail.message);
+    }
+    else if (e.detail.message.indexOf("failure:") == 0) {
+      ok(false, e.detail.message);
+    }
+    else if (e.detail.message == "finish") {
+      SimpleTest.finish();
+    }
+    else {
+      ok(false, "Got invalid message: " + e.detail.message);
+    }
+  });
+
+  /**
+   * file_browserElementOpen1 does
+   *
+   *   window.open('file_browserElement_Open2.html', 'name', 'features')
+   *
+   * then adds an event listener to the opened window and waits for onload.
+   *
+   * Onload, we fire a few alerts saying "success:REASON" or "failure:REASON".
+   * Finally, we fire a "finish" alert, which ends the test.
+   */
+  iframe.src = 'file_browserElement_Open1.html';
+  document.body.appendChild(iframe);
+}
+
+runTest();

new file mode 100644
--- /dev/null
+++ b/dom/browser-element/mochitest/browserElement_OpenWindowRejected.js
@@ -0,0 +1,44 @@
+/* Any copyright is dedicated to the public domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// Bug 742944 - Do window.open from inside <iframe mozbrowser>.  But then
+// reject the call.  This shouldn't cause problems (crashes, leaks).
+
+"use strict";
+SimpleTest.waitForExplicitFinish();
+
+function runTest() {
+  browserElementTestHelpers.setEnabledPref(true);
+  browserElementTestHelpers.addToWhitelist();
+
+  var iframe = document.createElement('iframe');
+  iframe.mozbrowser = true;
+
+  iframe.addEventListener('mozbrowseropenwindow', function(e) {
+    ok(e.detail.url.indexOf('does_not_exist.html') != -1,
+       'Opened URL; got ' + e.detail.url);
+    is(e.detail.name, '');
+    is(e.detail.features, '');
+
+    // Don't add e.detail.frameElement to the DOM, so the window.open is
+    // effectively blocked.
+  });
+
+  iframe.addEventListener('mozbrowsershowmodalprompt', function(e) {
+    var msg = e.detail.message;
+    if (msg.indexOf('success:') == 0) {
+      ok(true, msg);
+    }
+    else if (msg == 'finish') {
+      SimpleTest.finish();
+    }
+    else {
+      ok(false, msg);
+    }
+  });
+
+  iframe.src = 'file_browserElement_OpenWindowRejected.html';
+  document.body.appendChild(iframe);
+}
+
+runTest();

new file mode 100644
--- /dev/null
+++ b/dom/browser-element/mochitest/browserElement_OpenWindowRejected2.js
@@ -0,0 +1,48 @@
+/* Any copyright is dedicated to the public domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// Bug 742944 - Do window.open from inside <iframe mozbrowser>.  But then
+// reject the call.  This shouldn't cause problems (crashes, leaks).
+//
+// This is the same as OpenWindowRejected, except we "reject" the popup by not
+// adding the iframe element to our DOM, instead of by not calling
+// preventDefault() on the event.
+
+"use strict";
+SimpleTest.waitForExplicitFinish();
+
+function runTest() {
+  browserElementTestHelpers.setEnabledPref(true);
+  browserElementTestHelpers.addToWhitelist();
+
+  var iframe = document.createElement('iframe');
+  iframe.mozbrowser = true;
+
+  iframe.addEventListener('mozbrowseropenwindow', function(e) {
+    ok(e.detail.url.indexOf('does_not_exist.html') != -1,
+       'Opened URL; got ' + e.detail.url);
+    is(e.detail.name, '');
+    is(e.detail.features, '');
+
+    // Call preventDefault, but don't add the iframe to the DOM.  This still
+    // amounts to rejecting the popup.
+    e.preventDefault();
+  });
+
+  iframe.addEventListener('mozbrowsershowmodalprompt', function(e) {
+    var msg = e.detail.message;
+    if (msg.indexOf('success:') == 0) {
+      ok(true, msg);
+    }
+    else if (msg == 'finish') {
+      SimpleTest.finish();
+    }
+    else {
+      ok(false, msg);
+    }
+  });
+
+  iframe.src = 'file_browserElement_OpenWindowRejected.html';
+}
+
+runTest();

new file mode 100644
--- /dev/null
+++ b/dom/browser-element/mochitest/file_browserElement_Open1.html
@@ -0,0 +1,33 @@
+<html>
+<body>
+<script>
+
+// Because this file is inside <iframe mozbrowser>, the alert() calls below
+// don't trigger actual dialogs.  Instead, the document which contans the
+// iframe receives mozbrowsershowmodalprompt events, which the document uses
+// to determine test success/failure.
+
+function is(x, y, reason) {
+  if (x === y)  {
+    alert("success: " + x + " === " + y + ", " + reason);
+  }
+  else {
+    alert("failure: " + x + " !== " + y + ", " + reason);
+  }
+}
+
+function ok(bool, reason) {
+  alert((bool ? "success: " : "failure: ") + reason);
+}
+
+var w = window.open("file_browserElement_Open2.html", "name", "features");
+w.addEventListener("load", function() {
+  ok(true, "got load");
+  is(w.opener, window, 'opener property');
+  is(w.location.href, location.href.replace('Open1', 'Open2'), 'correct location');
+  is(w.document.getElementById('testElem').innerHTML, 'test', 'elem innerHTML');
+  alert("finish");
+});
+</script>
+</body>
+</html>

new file mode 100644
--- /dev/null
+++ b/dom/browser-element/mochitest/file_browserElement_Open2.html
@@ -0,0 +1,5 @@
+<html>
+<body>
+<div id='testElem'>test</div>
+</body>
+</html>

new file mode 100644
--- /dev/null
+++ b/dom/browser-element/mochitest/file_browserElement_OpenWindowRejected.html
@@ -0,0 +1,16 @@
+<html>
+<body>
+
+<script>
+var w = window.open('does_not_exist.html');
+if (!w) {
+  alert("success:w is null");
+}
+else {
+  alert("failure:w is not null -- " + w);
+}
+alert("finish");
+</script>
+
+</body>
+</html>

--- a/dom/browser-element/mochitest/file_empty.html
+++ b/dom/browser-element/mochitest/file_empty.html
@@ -1,10 +1,12 @@
 <html>
 <body>
 
+<!-- Tests rely on the fact that there's an element in here called 'url'. -->
 Aloha!  My URL is <span id='url'></span>.
+
 <script>
 document.getElementById('url').innerHTML = window.location;
 </script>
 
 </body>
 </html>

new file mode 100644
--- /dev/null
+++ b/dom/browser-element/mochitest/test_browserElement_inproc_OpenWindow.html
@@ -0,0 +1,13 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test of browser element.</title>
+  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="application/javascript" src="browserElementTestHelpers.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<script type="application/javascript;version=1.7" src="browserElement_OpenWindow.js">
+</script>
+</body>
+</html>

new file mode 100644
--- /dev/null
+++ b/dom/browser-element/mochitest/test_browserElement_inproc_OpenWindowRejected.html
@@ -0,0 +1,13 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test of browser element.</title>
+  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="application/javascript" src="browserElementTestHelpers.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<script type="application/javascript;version=1.7" src="browserElement_OpenWindowRejected.js">
+</script>
+</body>
+</html>

new file mode 100644
--- /dev/null
+++ b/dom/browser-element/mochitest/test_browserElement_inproc_OpenWindowRejected2.html
@@ -0,0 +1,13 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test of browser element.</title>
+  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="application/javascript" src="browserElementTestHelpers.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<script type="application/javascript;version=1.7" src="browserElement_OpenWindowRejected.js">
+</script>
+</body>
+</html>

new file mode 100644
--- /dev/null
+++ b/dom/browser-element/mochitest/test_browserElement_oop_OpenWindow.html
@@ -0,0 +1,13 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test of browser element.</title>
+  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="application/javascript" src="browserElementTestHelpers.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<script type="application/javascript;version=1.7" src="browserElement_OpenWindow.js">
+</script>
+</body>
+</html>

new file mode 100644
--- /dev/null
+++ b/dom/browser-element/mochitest/test_browserElement_oop_OpenWindowRejected.html
@@ -0,0 +1,13 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test of browser element.</title>
+  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="application/javascript" src="browserElementTestHelpers.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<script type="application/javascript;version=1.7" src="browserElement_OpenWindowRejected.js">
+</script>
+</body>
+</html>

new file mode 100644
--- /dev/null
+++ b/dom/browser-element/mochitest/test_browserElement_oop_OpenWindowRejected2.html
@@ -0,0 +1,13 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test of browser element.</title>
+  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="application/javascript" src="browserElementTestHelpers.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<script type="application/javascript;version=1.7" src="browserElement_OpenWindowRejected.js">
+</script>
+</body>
+</html>