I've been trying out Firefox for about a month or so now.
I've got to say that it's a pretty good browser. Certainly seems to have less problems with spyware, popups and the like than IE.
But lately, I've been reminded about why I switched to using IE after 5 came out in the first place. When I use IE, that's all I need to use. When I use Firefox, there's plenty of websites out there that I still need IE to use properly. Some examples are Windows Updates, the web interface of our Netscreen firewall, the Trend Micro online virus scanner, and Yahoo Games.
So while Firefox is in many ways the better browser, it certainly isn't the more standard browser. Everyone makes sure that their sites work for IE (if you don't you shouldn't be building web sites, unless you want most of the people of the world to NOT visit your site) but not so for Firefox.
Having said that, I will continue to use Firefox where I can, but anyone who makes it out to be the end all-be all web browser is smoking some good stuff and needs to look at the facts instead of just wallowing in their emotional response to Microsoft.