Hi, no idea on Sync, do not use it, but will give you some info : 1 ) if not using to sync 2 devices then stop using it as it is not meant to be a backup tool and will eventually loose your information and we will tell you the above and that it is gone and no way to get it back. 2) This is all I have on Sync : *https://support.mozilla.org/en-US/kb/how-do-i-set-sync-my-computer *https://support.mozilla.org/en-US/products/firefox/sync *https://support.mozilla.org/en-US/kb/how-do-i-choose-what-types-information-sync-firefox *https://support.mozilla.org/en-US/kb/firefox-sync-troubleshooting-and-tips *https://support.mozilla.org/en-US/kb/change-primary-email-address-firefox-accounts Only if there is a Issue you can confirm : You can open about:sync-log via the location bar to see if there are recent error logs available. You can upload a recent log if the log is too big to put in a reply. https://pastebin.mozilla.org/ 3) As for manually I suggest it strongly, more than strongly : *https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles *https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer Please let us know if this solved your issue or if need further assistance.