Firefox lost all session data after an update to 61.0 and a subsequent system reboot. No browser windows have been closed before the reboot. When I started Firefox again the "Restore previous session" option was greyed out and in the folder sessionstore-backups there were only two files "recovery.baklz4" and "recovery.jsonlz4". Both didn't contain any useful data. Is this a known bug? Can I still do something to restore the previous session?