Firefox 3.
I did a phased switchover, where I ran Firefox 3 on my Laptop and Firefox 2 on my PC, and I found it hard to use Firefox on my PC after a while, which is when I decided to fully switch to Firefox 3. I really like the new address bar feature, where it searched your history and bookmarks, without needing to actually type the first part of the url in.
QUOTE (Gee @ Sep 21 2008, 05:55 AM)

I use FF3, I haven't used FF2 yet.
If your using Firefox 3, I doubt you'll ever use Firefox 2.

Also, technically this should be in Polls & Surveys, however it is more than just a poll right now, and there is discussion going on, I will leave it be in Tech Discussion.