16 
A plug here for an excellent Firefox extension - Firebug. Designed to help facilitate web development, it shows you the html in a webpage, any javascript it's running, xmlHttp requests and more!
5 
Just found a very useful Firefox add-on, well, useful for webmasters with advertising on their websites. This displays your adsense earning at the bottom of your browser, updating itself periodically.
26 
The new downloads are out! To be honest, I wasn't a big fan of Firefox 1.0. It was so slow at start up, taking about 10 seconds or more and kept crashing, so I stuck with Internet Explorer. Firefox 2.0 however? The jury's still out. Now that IE has the <sarcasm>incredibly innovative</sarcasm> addition of tabbed browsing, is there much point?
There's a good article here reviewing the rival browsers.