Moving Firefox profile to new computer

1. Completely close firefox on your old computer
2. Copy the profile folder on old computer (C:\Windows\Profiles\\Application Data\Mozilla)  to the location where you want to new computer C:\Windows\Profiles\\Application Data\Mozilla.
3. Start the Profile Manager by typing the following in Start firefox.exe -P
4. Click on the "Create Profile..." button.
5. In the dialog that opens, enter a descriptive name for the profile.
6. Click on the "Choose Folder..." button. A "Browse for Folder" dialog will open.
7. Select the profile folder you copied and click OK.
8. Review the path shown in the "Completing the Create Profile Wizard" dialog to make sure it is correct, then click "Finish" to create the new profile.
9. Select the new profile and press the Start button to start Firefox using the moved profile.

Source
http://kb.mozillazine.org/Moving_your_profile_folder