if all you want is a browser firefox is what you need.
advantages are practical, financial and philosophical.
1) tabbed browser ( like opera)
2) relatively immune to viruses/malicious code
3) easy to control cookies & javascript
4) a variety of different skins (icons/colours etc)
5) more standards compliant than IE
6) encourages users to get involved.
If you need a mail client and newsgroup reader the full mozilla is what you need