User Agent: Mozilla/5.0 (Windows NT 6.1; rv:36.0) Gecko/20100101 Firefox/36.0 Build ID: 20150305021524 Steps to reproduce: Pressed "x" on the right side of a tab to close it, but the visual display of the tab and all of its contents remain. Double clicking the top of the window to cause Firefox to go full screen will cause the tab to disappear. So it's as if a needed redraw did not occur without forcing it. This issue is intermittent and happens roughly once per hour of usage. I haven't found a reliable way to reproduce it but I experience it every single day with normal usage. It's a recent regression (perhaps within the last ~2 months?). Actual results: The tab remains after being closed, though if I recall you can't interact with it. Also opening a new tab will cause the new tab to display on top of the remnant one. Expected results: The tab should have gone away.