What is a Firefox Profile?

Firefox allows to create different profiles. Each profile stores its own customizations, bookmarks, extensions. Personally I will use secondary profile to try new extensions before installing it in my primary profile.

Firefox stores default profile at "C:\Documents and Settings\USER_NAME\Application Data\Mozilla\Firefox\Profiles" in windows XP. (http://kb.mozillazine.org/Profile_folder - See the link for other OSes).

You can create new profile in different drive other than the root partition, so that even if your windows crash your profile will be safe.

Open Windows Run (Win + R) and type Firefox -p. Profile manager will be opened. It will allow you to create new profile, to rename, and to delete a profile. To create new profile, it will asks for a name. It usually creates new profile in the root partition. Select different partition by clicking on Change Folder. If you give your existing profile folder name, it will use the existing settings.

Thats it. You can create any number of profiles. If you don't have Firefox already, get Firefox now.