I know it seems as if I work for Mozilla, but I'm going to have to disagree.
One of the biggest features of Firefox that makes it better is security. It's quite simple to realize that since IE is the standard for internet browsers, almost all websites that feature malicious code or worms will design their attacks for flaws in the IE structure. Although it's possible to stay ahead of that trend by constantly updating IE or having excellent anti-virus software installed, you can rest easy knowing that Firefox is secure on its own.
It's popup blocker is also superior to IE's and it's interface is constantly being updated to accomodate more and more IE-only websites.
The find feature is also amazing. I use it quite extensively, and in IE where a box pops up and you can only search for one instance of a word at a time, in Firefox, there is a toolbar at the bottom of the window that you can use to search AND highlight multiple words in a document. This comes in handy at times for me while searching through FBC!
Extentions are the coolest thing to ever hit a web browser, something IE doesn't support. Since Firefox is open source, it is open to modifications from people all over the internet. The Firefox website includes and extensive list of extensions that enhance the functionality and the usefulness of the browser.
It is also skinnable, unlike IE.
RSS feeds (it's complicated, so I won't get into here) are also supported unconditionally in Firefox.
So, the new IE 7 is supposed to closely resemble Firefox... but what puts firefox over the top for me are the extentions. It's so customizable, you'll wonder why you ever used IE to begin with. Just give it a chance. It's completely free and easy to uninstall if you don't like it.