firefox beta 4Can you switch back and forth between Firefox 3 and 4 beta?

I am thinking of installing Firefox 4 beta but I would like to know if it replaces 3 or can you easily go bacfirefox beta 4k in case of problems. I know I can reinstall 3. I want to know if 3 remains without reinstalling it.
it will firefox beta 4replace 3. but if u want to go back, just download firefox 3 again, remove forefox 4 and install 3 again