I used to use IE when we got our first computer. Found out about Firefox on some forum site about a year ago and have used it since.
I like the look of it better, it's a bit faster for me, and the add ons seem to give you more control over it.

Just out of curiosity, how many different browsers are there?
I've only really heard of IE, Firefox, Opera and Netscape.

Oh, and is it really worth changing to Opera? Some seem to think it's a lot better than Firefox.