Firefox has far more functionality, is more robust and is generally a lot more fun to use than IE. The most important FF feature bar none is tabbed browsing. The fact that IE does not have it is a scandal. It would be as if most people were driving around in Model Ts when a Porsche was available. But there are myriad additional features available to FF, which IE has never heard of. In addition, you can customize added features and graphic displays available in FF with the 120 extensions and myriad themes available. If you haven’t seen or heard of Firefox, I strongly recommend you at least look over a demo if not download it.
In all candor, I do have to add a note of caution. Firefox is much more stable and trouble-free than it was when I first began using it–but it is not yet comparable to IE in those categories. It does have bugs and some of them are troubling. But one must keep in mind that unlike Microsoft, Mozilla is a company whose products are entirely driven by volunteers. As such, things work a little differently than with Windows products. With Firefox, you have to spend more time post-installation with operating and maintaining your browser. I’m not saying that this burden is overly onerous or forbidding; but it does take some work.
Another issue facing FF is that there are a number of websites that have not been designed with FF in mind and do not take well to it. So you may find some odd behaviors with such sites. But with every new FF user this will become less and less a problem.
So if you want a boring, feature-poor product that is relatively stable (but certainly not as secure as FF), go with IE. If you want a feature-rich browser that does much more than you could ever possibly need it to do, go with Firefox.