It's an excellent browser with only one pitfall: as far as I'm aware, you still can't browse full-screen with a "auto-hide" toolbar which will appear and disappear when you move the mouse to and from the top of the screen.
If you don't care about full screen browsing and you're happy with Mozilla then keep it. There's no reason not to like it: it's a fine browser, though not all sites support it yet and you might have minor problems with complex sites that haven't coded for Mozilla. It also opens slower than IE because IE is loaded into memory when Windows starts but, that's irrelevant after the browser is open and it's not so bad as to be annoying.....it's just something I've noticed.
Those of us who appreciate full screen browsing with auto-hide have to stick with IE until Mozilla supports the function. That's the biggest downside right now.
As for "Stopping popups" IE did this without third party software. It's amazing how many people are ignorant of the fact but I discussed it here today.
Mozilla seems to be able to tell the difference. It's sweet.