which browser extensions do you use?

[Namreg]

i recently found a useful firefox extension through a friend, and it got me thinking: why not make a thread so we can all share and hopefully learn something!

the two i use right now:
- Premium Link Upgrade blocks most ads on webpages
- Premium Link Upgrade removes the time limits imposed by megavideos and veoh. quite useful for people like me who refuse to watch television.