I just want to echo the Adblock with Filterset G updater. I can't remember the last time I saw a banner ad.
Two others I use:
Tweak Network 1.1 (optimizes Firefox settings based on the speed/power of your PC and your bandwidth speed)
CookieCuller (Extended cookie manager) You can select cookies to permanantly keep, such as login cookies. Used in conjuction with FF's cookie managment. If you select "delete all cookies on exit" CC will override that and retain all protected cookies you flagged. Very helpful!]
Also, you may want to think about customizing the search engines available to you (right hand side of the browser). I added Wikipedia, which I have since found indespensible.
Who are you going to believe, me or your own eyes?