In your home directory, you'll have a hidden directory called ".mozilla". This contains all your user specific stuff. Copy that, and it theoretically should set your new mozilla up the same as your old.
One caveat, of course. There have been a number of changes to Mozilla, and there's the risk that some of the options either don't transfer, or are transferred in unexpected ways because of different formatting or added/removed/altered options. So, though this should work fine, you're still probably going to want to do some checking (in preferences) to make sure it's how you want it. In rare cases (I haven't encountered this in a production version yet, it's usually only in the nightlies that you see it), your options might scramble your settings or cause problems with the browser.
Not really something to worry about, but something to keep in mind.