All-in-One Sidebar – this one is nice for my widescreen monitor – shifting realestate from the top to the side.

Tree Style Tabs – same as the sidebar – much more orderly now that I’m used to it and keeps the shape of my actual browsing space taller.

Xmarks – this is another must – keeps all my bookmarks synced between my laptop and desktop

TwitterBar – easy twitter posts right from the FF address bar.

Zementa – I have this but don’t really use it much. Yet.

SmarterFox – this one is actually sort of useful, but I haven’t gotten in the habit of making the most of it.

Personas for Firefox – quick way to keep Firefox looking good

Cooliris – very nice image viewer but this one is on the chopping block. Get it and use it if you like looking at pictures. A lot. And you don’t mind it being big, clunky, and not really integrated well with the browser.

Read it Later – I just began experiementing with this one. Lets you easily add links or pages to a list available for later viewing. Online or offline. List is synced with your other computers and mobile device.

Speed Dial – Every time you open a tab you see nine links with big thumbnails of your favorite sites.

That’s about it.