Firefox is a great browser no doubt, the thing that counts most (according to me anyways) is it's user community. People who use Firefox the most seem to be developers and so on. And with it's extension capability the developers can make extensions to make lives easier. So basically what I mean to say is that Firefox is going to have more features (extensions, if not in built) compared to other browsers. So naturally people are going to use it more and more as they get to know about it.

Oh yeah and let's not forget about the people who own Mac's as well... since they aren't' going to have IE 7, they are most likely going to pick Firefox (because Camino doesn't have extensions and Safari isn't compatible with many sites)...

And with FireFox 2.0 coming soon, I think the people who use Firefox are going to increase a lot, since it is probably going to have the capability of IE 7 and more.