Firefox is awesome.
Recently there have a been a ton of articles in the press about browser vulnerabilities (namely against IE, but some against Mozilla and Firefox, too). The thing is, at least Firefox is still in beta. IE, while I still like it, is at version 6 -- eloquently put in Mike's blog (here
Why Firefox is the cat's pajamas:
1. Tabbed browsing.
2. Extensions like User Agent Switcher and Web Developer. Check them out, it's amazing. There are hundreds of these extensions.
Why it's not everything:
1. ActiveX (specifically for Yahoo Launch -- gotta have it).
2. Microsoft Windows Update.