Wow! I'm starting to be blown away by Firefox... I installed two extensions today in particular that are pretty incredible.
The first is Sage
This is an RSS/Atom aggregator which is pretty slick. Once installed, you can bookmark RSS feeds and bring them up in a sidebar toolbar.
The other is FireFTP - a built in FTP client. Duhhhhh... M$FT are you watching? This is so simple and integrated it's amazing. I'm lovin it!