What are some good Firefox Add ons?
I have Adblock, but nothing else.
Flashblock.
Twitterfox and Anycolor.
I don't even know what Twitter is.
TabMixPlus
SessionManager
Greasemonkey
IETab
All-In-One Gestures
Leechblock
http://rikaichan.mozdev.org/ - The popup Japanese-Your Language dictionary (where your language can be English, French, Russian, German).
If you want a new skin, PitchDark or Blue Fox (there's a Red and Green variant, though).
XMarks for bookmark syncing/backup.
Read it Later.
NoScript, if you hate the ads, that sometimes escaped the AdBlock Plus list.
Though you have to manually one time enable some scripts if you're browsing video/media based sites like Youtube, Metacafe, etc due to the involvement of active scripts there.
Greasemonkey loads useful user made scripts (Like linkchecker) to your browser....