I switched my email to Mozilla Thunderbird, and I love it. So, it was natural that I use Firefox also - it is free, easy to download and easy to use.
Try it - give it the ol' wet test for a few days - you'll like it. If not, you always have IE to go back to. In fact, you never lose IE - it's always right there and they can both be open and running at the same time if you need.
I used to find sites which would not work in Firefox, but now they all seem to have dialed that in. The web pages I produce and manage are all optimized for Mozilla, and I know other web developers who do the same. In fact, Terminator's camera is the only thing I have to use IE for anymore...
8-)