I'm using Firefix 5.0 Many times when I play video stream on one tab and close it during the stream still running my system stopped working (I can move the mouse pointer but can't click on anything and none of keyboard button including the ctrl-alt-del worked also.) I got a suggestion from mozillazine forum to disable all add-on and it seems help. However I don't know how to set it permanently so it keeps freezing my system regularly. So I really need a better solution here. PS One time it even freezes my system while I did not run any video stream on it.