Update: µblock is the new AdBlockPlus.
This short post is just a quick collection of useful firefox add-ons for a more comfortable and privacy enhanced websurfing...
BetterPrivacy (for blocking flash cookies, i.e. local shared objects - so called long term cookies).
Ghostery for displaying and more importing also blocking tracking services.
Another add-on that's quite useful is some kind of gesture app, e.g. FireGestures.
For easily translating (parts of) a website: Quick Translator - uses google translate.