if you are tooooo fed up with having to do this create a 2nd firefox profile or (like me) run firefox 3.6 alongside firefox 5 dang you could even just use chrome & create a SSB for facebook & then do all your 'normal browsing' in a normal chrome session
hell if you are really into SSB's then use prism to create a SSB for facebook (if you love firefox) which by default uses a new profile for each SSB created
i know it is a bit arcane but you only need to do this once & facebook will be 'in a jail' lol
also most of the addictive games seem to run a bit smoother in 3.6
all i am saying is dont think that all you have to do is clear cookies or add a few addons as this is either a pain in the butt or makes firefox etc heavy
too many people forget there is more than 1 way to skin a cat