You do not need to backup or restore this ''lock'' file, it is only used to prevent more than one Firefox instance from using the profile at the same time, same for .parentlock ---- You can copy certain files with Firefox closed from one profile folder or backup to the current profile folder to recover your personal data. Note that best is to avoid restoring a full profile folder and only restore important files that are safe to restore/transfer. <hr> *bookmarks and history: places.sqlite *favicons: favicons.sqlite *bookmark backups: compressed .jsonlz4 JSON backups in the bookmarkbackups folder *cookies.sqlite for the Cookies *formhistory.sqlite for saved autocomplete Form Data *logins.json (encrypted logins) and key4.db (encryption key/primary password) for logins saved in the Password Manager *cert9.db for certificates stored in the Certificate Manager *persdict.dat for words added to the spell checker dictionary *permissions.sqlite for Permissions and possibly content-prefs.sqlite for other website specific data (Site Preferences) *sessionstore.jsonlz4 for open tabs and pinned tabs (see also the sessionstore-backups folder)