Favorite Firefox Extension…

just curious…what is everyone’s favorite Firefox extension.

My favorite is Adblock
Here is a breif description of the Adblock Extension:
If you’re tired of all the intrusive adverts that are increasingly taking over the Internet, Adblock is for you. Using the numerous free filter repositories available on the net and the intuitive blocking tools, you are able to customise your Firefox so that the most annoying ads are not displayed, thus leaving you to browse safely and to enjoy your Internet experience.