I just transferred FireFox from my Windows XP laptop to my Windows Vista desktop. I found some decent guides on the Internet, but none of them were complete.
Install Firefox onto the target computer. It should be the same version as your host computer.
Transfer your remote settings. In my case, it was
from C:\Documents and Settings\<username>\Application Data\Mozilla\Firefox\Profiles\q0dmgodo.default to C:\Users\<username>\AppData\Roaming\Mozilla\Firefox\Profiles\q0dmgodo.default
and transfer your local settings too. In my case, it was
from C:\Documents and Settings\<username>\Local Settings\Application Data\Mozilla\Firefox\Profiles\q0dmgodo.default to C:\Users\<username>\AppData\Local\Mozilla\Firefox\Profiles\q0dmgodo.default
Normally, just transferring the remote setting would be enough, but I wanted to move the data in Google Gears as well.
Rename the profile settings to the existing profile folders. I had to rename my folders from q0dmgodo to r6f5nkhv. If you forget to do this, you get an error message when you start FireFox saying “Firefox is already running but is not responding” because it can’t find the profile folder.