Your old archives still there are in your hard drive? If yes, try see these articles: *[https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them?esab=a&s=bookmarks+restore&r=1&as=s Restore bookmarks from backup or move them to another computer] *[https://support.mozilla.org/en-US/kb/recover-lost-or-missing-bookmarks Recover lost or missing Bookmarks] *[https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data Profiles - Where Firefox stores your bookmarks, passwords and other user data] *[https://support.mozilla.org/en-US/kb/Recovering%20important%20data%20from%20an%20old%20profile?esab=a&s=bookmarks+restore&r=5&as=s Recovering important data from an old profile]

On Linux you usually have the home directory mounted as a separate partition to prevent losing data when updating, so that only the partition with the system files needs to be reformatted. This should also work when downgrading. If you only had one partition for your personal data and the system files that you probably lost all you personal data in the home (~) directory. *http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox *http://kb.mozillazine.org/Profile_folder_-_Firefox