Firefox, how I love thee. I also love the extensibility of it. I test a lot of extensions, and some are more useful than others. Here is my list of extensions.
Upon examining this list I think there are a few I can get rid of after the upgrade to Firefox 2. Restart Firefox and the Google Toolbar come to mind. And I don't use the dictionary search any more.
The most useful extensions add-ons that I actually use pretty much every day: