Well, Mozilla is not going to break IE, and on most sites it works great.
Of course, some sites (more MS-oriented) will be Mozilla-unfriendly, but you can always fire up IE and copy/paste the link.
It's really only a question of personal preference. I used to use Netscape and avoid IE like the plague, until one day (way back when) I found out that my Netscape could no longer get me into my Netscape webmail - whereas IE could (yes, its true !!).
Floored by this revelation, I closed my Netscape account and switched halfheartedly to IE, which I have always viewed as a necessary evil.
Therefor, when Mozilla brought out version 1.6 and I learned about all the good things it brings (popup and ad-blocking notably), I downloaded it and gave it a try.
Haven't been disappointed since. No longer are there rogue cookies taking up my disk space. No more pop-ups or pop-unders of any kind taking my bandwidth without asking. I have even banned the ads from my most-used sites from ever appearing.
In short, there are many useability reasons for trying Mozilla, but the best reason is that NO AUTO-INSTALLING VIRUS code can graft itself to Mozilla without you knowing about it (and being able to stop it) !
Now, if that in itself is not a good reason to at least try, I don't know what else to say.
Pascal.