.mozilla is the main directory used for the Firefox Profile Folder You can use the Profile Manager to create a new profile for the Firefox 4.0 beta version. You should also create a desktop shortcut for both versions that specify the profile name as shown in the Profile Manager (-P "Profile name")

See: http://kb.mozillazine.org/Profile_Manager http://kb.mozillazine.org/Shortcut_to_a_specific_profile

Thanks for your reply, but since I am testing beta software, I do NOT want to use the same .mozilla directory -- there are other things in there, above the ???.default profile, which may or may not get scrambled (an extensions directory, for example).

What I have done temporarily is create a shell script that moves .mozilla out of the way, and renames .mozilla-beta to .mozilla while running the beta, then moves everything back when exiting. Inelegant, but effective.

I am still wondering if there is a way to get the beta copy to look somewhere else than .mozilla for its files.

If you want to keep them separate then easiest is to create another user and login as that user if you want to keep the beta version separate. There is nothing wrong with having multiple profile folders and different Firefox versions using the same .mozilla directory. You can even start multiple versions at the same time. That won't be possible if you do it your way. Seehttp://kb.mozillazine.org/Opening_a_new_instance_of_Firefox_with_another_profile

I have at least 7 Firefox versions from 2.0.0.x and 3.0.x to 3.5.x and 3.6.x (release and nightly build) and 4.0b2pre nightly builds installed for testing purposes. You only have to make sure that you launch each with its own profile and easiest to ascertain that is to use shortcuts or scripts that launch each of them using -P "Profile"

OK, sound like I will have to go with that.