User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:40.0) Gecko/20100101 Firefox/40.0 Build ID: 20150812163655 Steps to reproduce: Just open FF in either full screen or window Actual results: Clicking any of the 3 buttons at the top right of screen does nothing. Double clicking top line exits full screen mode OK but the only way to exit FF is to close each TAB in turn. Expected results: x= close - - minimise middle icon exit full screen First started when I upgraded to Windows 10 and updated FF to v40.0 v40.0.2 no change still a problem