Firefox 1.0 (Preview Release) is just out.
Stodgy as I am, I've been using Firefox 0.91 as my preferred browser at work for months now. It may be a little slower to load than IE, but it seems to render pages faster and is presumably (?) less subject to IE's various security problems.
It's worth a try. It's a relatively small download (1.0 is just under 5MB, a little smaller than 0.91), it has a nice set of features, and it does an excellent job of importing your IE bookmarks. I haven't explored the full range of features (for example, there's an "RSS" logo in the lower right hand corner of my screen as I write this, which invites me to "Add Live Bookmark for this page's feed"!), but it's powerful and a good alternative to IE. It's far more compatible than Opera, and doesn't have ads.
So why haven't I gone to Firefox completely--and why do I say "at work"?
Simple: the iNotes Web email client from IBM Lotus, which is how I get to Notes mail from home, won't run under anything but IE--and at work, Onyx (commercial software that we use for a variety of internal functions) won't work under anything but IE.
Such is life. (Eureka runs just fine on Firefox, if you're wondering...)