Hmm...

I think I downloaded quite a lot of stuff within the first three hours of my Firefox experience.

Noscript: essential; besides, it blocks some annoying ads out on its own.

Fasterfox: probably faster, I think, since I never used Firefox without it.

DownThemAll!: help for mass downloading stuff, which is useful, since I've been trying to build up a mini classical music library of my own for personal use. Wonderful , I now have unintrusive, soothing music that can sharpen my mind when I'm doing math, or typing, etc.

Adblock: what is there to explain? Essential, of course.

Adblock Filterset.G Updater: what's this extension for again? I have it, that's all I know.

FoxyTunes: just a little useless toy to play music while I surf. It looks cool, though.

Image Zoom: very useful for those annoying threads here with oversized -- or too small -- pics.

SearchPluginHacks: I felt a little miffed that I couldn't remove Yahoo, Answers.com, etc., out of the top-right corner search engine thingy, so I downloaded this one and annihilated it. Now I'm gonna remove it, though, no need anymore.