diff -r 000000000000 -r 6474c204b198 browser/components/preferences/in-content/tests/head.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/preferences/in-content/tests/head.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,35 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+function is_hidden(aElement) {
+  var style = aElement.ownerDocument.defaultView.getComputedStyle(aElement, "");
+  if (style.display == "none")
+    return true;
+  if (style.visibility != "visible")
+    return true;
+
+  // Hiding a parent element will hide all its children
+  if (aElement.parentNode != aElement.ownerDocument)
+    return is_hidden(aElement.parentNode);
+
+  return false;
+}
+
+function is_element_visible(aElement, aMsg) {
+  isnot(aElement, null, "Element should not be null, when checking visibility");
+  ok(!is_hidden(aElement), aMsg);
+}
+
+function is_element_hidden(aElement, aMsg) {
+  isnot(aElement, null, "Element should not be null, when checking visibility");
+  ok(is_hidden(aElement), aMsg);
+}
+
+function open_preferences(aCallback) {
+  gBrowser.selectedTab = gBrowser.addTab("about:preferences");
+  let newTabBrowser = gBrowser.getBrowserForTab(gBrowser.selectedTab);
+  newTabBrowser.addEventListener("Initialized", function () {
+    newTabBrowser.removeEventListener("Initialized", arguments.callee, true);
+    aCallback(gBrowser.contentWindow);
+  }, true);
+}