I just installed this - https://addons.mozilla.org/en-US/firefox/addon/433
prevents flash from loading by default, which as a frequent user of a few flash-ad-using sites i find extremely useful - it's already made a very noticeable difference to cpu and memory usage during web browsing. if you want to view it you just click on the icon where the flash content would be.

so far i've found the only places i actually needed to activate flash have been youtube, the occasional timewasting flash game/animation, and stupid corporate/marketing websites, which account for a tiny portion of my overall web usage.