You still have access to the old computer right? Did you use a Mozilla account on the old computer? '''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