I have been using FireFox
for a couple of weeks now. The implementation of Tabs and lack of clutter has me hooked. I am going to start testing a few of my ASP.NET apps and see if there are many issues with rendering. So far, things look I'll keep you posted.
So why are you using/not using FireFox? Can FireFox take a signfigant bite out of IE's market share? Its going to be interesting to watch.
Windows Media Player 10 will be available for download today at 6am P.D.T as announced by Microsoft.
Check out this PDF for a Features Overview.