It's a good idea to move this folder to another known place, in order to be able to back it up or move it to a new computer later!
The steps for moving/restoring the FF configuration directory are the same as the the Thunderbird steps, except that the location of the configuration directory is slightly different
C:\Documents and Settings\<your_login>\Application Data\Thunderbird
C:\Documents and Settings\<your_login>\Application Data\Mozilla\Firefox
about:profilesto change the default profile, at the bottom of the detailed TB page