What happened to Firefox 4?

I’m being nagged left and right to upgrade my machines. My main machine has Firefox 3.6 (due to plugin compatibility issues) but I upgraded several others to FF4. Now those machines are demanding to be updated to Firefox 5. And Firefox 6 is right around the corner. What the hell happened to 4? Was it that bad? Egad, I barely took the bubble wrap off the damn thing and now I have to upgrade again. And then upgrade again after that. Whoa there Mozilla, what the hell are you doing? You think you’re Chrome or something?