....Firefox 5?!?!? :blink:
Yeesh.
As for me, I use Firefox 3. I finally tried 4 last month, and almost immediately switched back - couldn't stand the changes they made to 4, all the junk they did to make it tab-centric (I really don't like tabs), along with the visual changes (the "no frame, floating glass window" thing) and the annoying alterations to menus (like the way the bookmarks menu didn't truncate long bookmark names anymore). When I hit the point that I was downloading the third addon to "fix" the changes they made, I realized I was being silly and should just keep using 3.