I don't really go for a lot of addons but do have a couple...

Downloadhelper> great for grabbing video or music

Glasser> Adds glass around firefox window

Adblock plus> of course

febe backup>for backing up all my settings and favorite addons

IMtranslator>translating language

Flashgot>Download all links etc..

Pixlr grabber> already mentioned




Ok, so maybe I do have more than a few after all. Didn't seem like it until I wrote them out. Oh, and my theme is "Gradient icool" Black and blue theme matches my whole PC setup.