Not security related though, but I just need to mention this awesome Firefox trick. It's about animated the most of the time annoying GIFs (.gif format of file); the thing is that to stop these GIFs animating one just needs to hit the Escape button (I've found out afterwards that it works also in Internet Explorer browser); I think that it works only on the current page/tab that one is on (i.e. the one with focus), and not on the whole window or even the whole Firefox instance (i.e. all the open tabs + all windows or in other words for the one particular "firefox.exe" process)

P.S. -- If anyone might want to, here is a link to a thread on Ars Technica tiled Firefox. Arrrgh! Why! FFS where I first saw it mentioned in in this particular Happysin's post (btw. my nick is "shirker" on Ars-forums)