Refer: https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
Source Computer
In Firefox click the pancake setting and go to Help, "More troubleshooting information"
Look for path to your "Profile Directory", such as:
/home/mruckman/.mozilla/firefox/6kzldk99.default-release
Close Firefox
Zip/Tar the entire folder
Target Computer
Same procedure as above, locate the folder of your profile. Erase everything in the folder and replace it with the source folder information, the contents remain the same, the only change is the folder name.
Make sure to CLOSE Firefox before deleting and copying the files