Bug 746977 - tree/test_cssoverflow.html ShiftTab not working, and a test timeout on OS X, disable

accessible/tests/mochitest/tree/test_cssoverflow.html

@@ -87,6 +87,13 @@
 
     function doTests()
     {
+      // Shift+Tab not working, and a test timeout, bug 746977
+      if (MAC) {
+        todo(false, "Shift+tab isn't working on OS X, needs to be disabled until bug 746977 is fixed!");
+        SimpleTest.finish();
+        return;
+      }
+
       gQueue = new eventQueue();
 
       // CSS 'overflow: scroll' property setting and unsetting causes accessible