You can copy certain files with Firefox closed from one profile folder to another profile folder to transfer personal data. Note that best is to avoid restoring a full profile folder and only restore important files that are safe to restore/transfer. *https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data *https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile *https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them <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)