Here are a few ideas from the experts:
Firefox keeps user profiles in a specific location. Each user has her own profile location in Windows 2000 and Windows XP, although users can choose to share profiles.
The prefs.js file is used to hold preferences that override Firefox's factory defaults.
The user.js file contains preferences that override both Firefox's factory defaults and any preferences set in prefs.js.
userChrome.css lets the user customize how Firefox looks. Much of the way Firefox looks can be customized in this file. You could create your own mini-theme using just userChrome.css.
userContent.css establishes the basic look for a web page. All formatting in the web page overrides this file's defaults.
Mozilla uses profiles to contain information specific to a user. Profiles can be shared and backed up or restored as necessary.
Users can have as many profiles as they want. The Profile Manager enables users to switch profiles when starting Firefox.
A profile can easily be cloned by copying the profile folder to a new name and editing the profiles.ini file to include this newly created copy of the profile.
If you delete the Mozilla Firefox folder in the program files folder without uninstalling Firefox, and then you reinstall Firefox, the new installation will use the existing profiles and settings.
Uninstalling Firefox does not remove profiles or profile information. If you want to uninstall Firefox and get rid of everything, you must manually delete the profiles.
When you upgrade Firefox, you should first remove all the extensions and themes. Sometimes an upgrade of Firefox is not compatible with some existing themes and extensions.
There is limited sharing of profiles between Firefox and Netscape 7.x. Profiles can be shared across platforms (such as Linux and Windows) if the user desires.