User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:11.0a2) Gecko/20120116 Firefox/11.0a2 Build ID: 20120116042010 Steps to reproduce: Windows 7 64 bit (clean load with Nvidia drivers) Nvidia GTX 560Ti 1) Click RSS feed button in toolbar Feed: location: http://fxfeeds.mozilla.com/en-GB/firefox/headlines.xml Site location: http://www.bbc.co.uk/go/rss/int/news/-/news/ 2) Click away from RSS drop-down box. Actual results: The feed's drop-down box is longer than Firefox window so it occupies from the Firefox toolbar down to bottom of screen overlaying desktop items and Windows toolbar. This is as expected. When clicking away from the feed's drop-down box it is removed from the main Firefox window but persists from top of the Firefox window's bottom border to the top border of Windows toolbar. Moving any application's window clears the drop-down artefact from the Windows toolbar but leaves it on the desktop. The artefact can only be cleared by moving the window of any application across the artefact or by pressing the "show desktop" icon. (Also 8 branch but not 3 branch). Expected results: The entire drop-down box should have been removed.