I switched from IE to Firefox years ago. (I also use Thunderbird for mail.) No major frills... very user friendly - intuitive. I switched for security.. I got tired of the pop ups and the spyware and the trojans I picked up everywhere in IE. Just with basic security settings in Firefox I don't pick up spyware anymore unless one of the kids intentionally downloads something. No more surprises. I'm sure that will change as Firefox becomes more and more popular - but for now it's exactly what I was looking for.
Pros: Faster. More secure. Neat convenient features like tabbed browsing. (Takes some getting used to but really nice when you've got a lot of windows open!) and the Download Manager -- no more searching your computer for wherever you downloaded something... The download manager pops up after every download with the location and the option of opening from the manager window.
Cons: There are still a few multi-media sites that aren't compatible with Firefox (although they say they are). What usually happens is you go to a site with video, etc. and you are told you need to download a plug-in -- even though you already have the plug-in.... For such instances I have to switch to IE if I really want to use the site. But those are becoming more and more rare as sites catch on.
If you try Firefox and you like it -- I do suggest using Thunderbird for mail as well.... The built-in mail filter options are super easy to use!
If you have men who will exclude any of God's creatures from the shelter of compassion and pity, you will have men who will deal likewise with their fellow men. -- St. Francis of Assisi