Problems with Firefox?

I had version 3.6.6. Worked great. No problems at all. Then I saw that version 5 was out so I decided to download it. Lo and behold it is full of various problems. One of the most annoying was that when I went to click the exit button, it wouldn't work. I'd have to repeatedly click it until the program quit responding and then exit. I really disliked the new layout and this particular problem was more than I could deal with, so I downgraded. Wouldn't you know it screwed that up too. I'm encountering the same problem with version 3.6.6. now. Why does it do this and how can I fix it?