Thanks for the update. Interesting thread.
I use both IE6 and Firefox - IE at work, Firefox at home (sometimes IE for banking, etc.). Both browsers reside just fine on both my home notebook and desktop and each one is set to check that it's the default - makes switching between the two very easy. When I have to use IE at home, can open and use it for that session and get everything just fine. Then close IE, open Firefox, and it's the default browser again.
One of the things about Firefox that is a big plus is Adblock - no flash ads (those Shopzilla things drive me crazy on IE and they ain't getting my business), able to block adds by website or by ad provider, etc. Very nice and clean web pages without all the ads.