Since everyone else is doing it, why not me. Here are the Firefox extensions I'm using (thanks to the ListZilla extension, exporting the list was simple):
Copy Links 0.1.3
PDF Download 0.6
Saferfox Xpanded 3.2.2
Tab X 0.9.2
Tabbrowser Preferences 188.8.131.52
Web Developer 1.0.1
I've pared down my extensions to the ones I really use regularly. It's always a bit addictive to go finding and adding new ones, but the more you have the slower Firefox will run. At one point I was up to about 25 extensions and FIrefox was crawling and behaving oddly.
I'd recommend using ListZilla to periodically export your list in case you have to do a new Firefox install. It can be a pain trying to remember which Firefox features are standard and which are extensions.