I think I'm done with Mozilla, and the stupid version numbering is just the last straw. Since they decided to start hyping up their version numbers, the quality of their products has gone down. They introduced a "feature" back in 3.6.xx that is completely annoying, and there are a lot of people complaining about it on the various help forums. It wasn't fixed in Firefox 4 or 5.
Now they've practically made Thunderbird unusable after jumping from version 3 to 5. The went overboard with the aero glass, so much that if you have a dark background, the menu and buttons are unreadable. Just look at this.