I'm late to the game, but I'm a Firebird zealot.
As a web developer, I find if I develop to standards, my pages work in IE and Mozilla (and even Opera).
As a web developer, I find if I developer for IE, my pages rarely work correctly in Mozilla (and Opera).
Moral of my story: develop for standards. It's what the future is based on. If you code for IE only, then your page will work for IE only, and you cut out that many people. Same sorta goes for flash-only websites, but that's another thread.
And Grey Ninja forgot the second best feature of Mozilla/Firebird after pop-up blocking: ad blocking. Through the use of image blocking (right click on an ad, and if the server is something like ads.server.com, block it) and this CSS file on
FloppyMoose.com, I rarely see an ad.
For the people that complain that Firebird doesn't display a certain page correctly, it's likely the fault of the developer who didn't spend the time to test it on other browsers.
Go ahead and stay with IE folks. When MS doesn't deliver an update and your browser is as functional as Netscape 4 is today, ha. I laugh at you. =)
If Firebird isn't your thing, check out Opera.