While watching youtube video from youtube.com in full screen mode (this is flash player full screen mode, not browser full screen mode), if you exit the full screen mode, some times the original page when the full screen was started from would stop drawing, not responding to the mouse click in the page area. The page will go back to normal if you click and drag the firefox browser title bar or just resize the browser window. I initially found this issue with our company's browser plugin product when testing on Firefox 4. Then I went on trying the same scenario with youtube flash player, it is the same behavior. It is not difficult to reproduce, if exiting full screen works fine, move the browser window a little bit and try it again. I can reproduce this once every 5 - 10 times. It is very annoying. The same test case works on Safari, Google Chrome without any problem. Please fix this!