I've been using Firefox for a number of months now and there is no way I would go back to Internet Explorer. The only time I use IE is for Windows updates, as it's the only browser you can use for that purpose.
The only way you will decide whether it's for you, is to try it. It will run happily along side IE and indeed on occasions I have run both simultaneously.
For me, the largest advantage is its ability to virtually block all spyware and Trojans. Whereas I used to scan nightly for spyware, once a week is all that's needed with Firefox and even then, I rarely find anything.
Add to that built a in pop-up blocker, tabbed browsing (how did we ever manage without that?) and other features to numerous to mention, makes this a first class browser.
This post is being written in Firefox with the Spellbound extension, checking my somewhat erratic spelling!