There is a new sync feature available by default with firefox 4, you may be interested in that. There are also other editions of firefox that are portable, and can be installed on a USB stick for instance.

The default location of the profile will not be ?c:desktop?, and if Windows crashes you will need to recover before you can use firefox.

It is however sensible to backup your profile, and you can back it up to or use it from almost anywhere see https://support.mozilla.com/en-US/kb/Backing%20up%20your%20information#w_restoring-to-a-different-location you can use the profile from a USB stick for instance, but there are slight problems with the way Windows assigns drive letters as you plug in and unplug drives. The easiest solution may be to leave the profile where it is, or move it to another fixed drive, and make a backup somewhere else.

You can move the Profile folders to anywhere you want them, but the profiles.ini file is still going to be in the \user\application data\Mozilla\Firefox file path. That file is the "controller" for the Profiles.

http://kb.mozillazine.org/Moving_your_profile_folder