Sync is you friend... This way you old computer can keep your data like a backup. I would also advise that you run 2 different versions of Firefox so that your data is in more than one place. Sync will see the different version(s) as different devices.see screenshot https://support.mozilla.org/en-US/kb/how-do-i-choose-what-information-sync-firefox https://support.mozilla.org/en-US/kb/how-do-i-set-sync-my-computer