Sync isn't use for backups for that you need to know about these Firefox help options below to backup data/profile/links to file or html or csv file to restore incase your computer is reformatted or you need to move that data to new computer. These are not in order but you should readup on them. Could be more I missed but these should be a starting point. https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles "How do I save my Firefox profile data" https://support.mozilla.org/en-US/questions/1381158 https://support.mozilla.org/en-US/kb/how-restore-browsing-session-backup " How do I backup a session (all the open tabs) so that it can be reloaded after a computer factory reset?" https://support.mozilla.org/en-US/questions/1257866

Keep in mind that Sync isn't designed to be used as a backup, but merely is meant to sync data between connected devices. Best is always to backup your personal data locally. *https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles *https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile