Adding a new profile to Firefox by cloning another

When you want to use Firefox with other settings you have to have additional profiles.

A good article about it (polish):
http://webmade.org/porady/mozilla-firefox-profile.php

After you added a profile you can copy all the contents of the other (previous) to have all extensions/settings/.... in the new one. It works. Then I could modify the contents to satisfy my needs.

Remember to close Firefox when using the commands to take effect while creating a profile.