These setting should be set on the computers, sign into the same account on both computers, and that's it. As a test download another version of Firefox [https://www.mozilla.org/en-US/firefox/channel/desktop/ (Beta, Dev, or NIghtly)] on the old computer and see if you can sync it. Sync info... '''FYI... Firefox Sync IS NOT A DATA BACKUP SERVICE''' https://support.mozilla.org/en-US/kb/how-do-i-set-sync-my-computer https://support.mozilla.org/en-US/kb/how-do-i-choose-what-information-sync-firefox https://www.mozilla.org/en-US/firefox/features/sync/ https://hacks.mozilla.org/2018/11/firefox-sync-privacy/ '''Sync is not a backup tool but it is a good sync/transfer/move tool''' https://support.mozilla.org/en-US/forums/contributors/707681