Sign into the same Mozilla account. I run all versions of Firefox and Waterfox on all laptops and Android devices. see screenshot Just an FYI... '''SYNC IS NOT A DATA BACKUP SERVICE''' Sync info... 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