Name some specifics instead or vague grumbling.
Version 1.5 had significant memory leaks. 1.5 would also "lose" bookmarks. I got rid of that and went back to 1.07. No problems with that build. 2.0 just crashes every so often. I have no idea what's causing it. Mostly when I go to specific news-oriented web sites. After FF crashes it'll allow me to bring up the previous session, tabbed browsers and everything, so that's an improvement over leaky 1.5 but my confidence isn't there. I try to use IE as little as possible. I've never used v7.0. Funny how some Firefox fanatics come off as the moveon.org types, all in your face about what MY problem is. It's irritating. You don't know my setup and I didn't code the dang browser.
I'm not a lucky person and my cheap-ass home computers are all "mongrel" home-brew machines that I have put together using my favorite components (cherry picking) from the ground up, so I should have been "bitten", but it hasn't happened.....yet.
At work, we have Firefox 2.0 on 76 machines (various manufacturers) and with very much non-tech people using them and the only complaint I've received so far was from a user who said "the mouse-pointer went off the screen and now I can't do anything!"...but that's nothing really new.