Switching between different versions of Firefox



I have different versions of Firefox installed on my Mac as I need to make sure my sites work correctly in them.

The problem that I have is that when I switch back from newer versions to older ones, my saved cookies and passwords keep getting zapped. I've temporarily got around the problem by using fast user switching to only run one copy of Firefox in any particular account, but it's fairly tedious to keep going back and forth while I'm testing style sheet layouts, etc., because I have to keep entering the password every time.

I don't necessarily need each copy of Firefox open at the same time (which doesn't seem to be allowed anyway if it's the same user) but I would like some way to at least be able to open different versions without them affecting each other - I've never seen any kind of user "profile" options in Firefox, so I assume it just creates one folder for each user.