If you have a "C:\Windows.old" folder with personal data from a previously installed Windows version then you can recover personal data from a previously used profile in this backup. * C:\Windows.old\Users\<user name>\AppData\Roaming\Mozilla\Firefox\Profiles You can copy files like these to the current Firefox profile folder to recover specific data. *bookmarks and history: places.sqlite *bookmark backups: JSON backups in the bookmarkbackups folder *SQLite files like cookies.sqlite (cookies) and formhistory.sqlite (saved form data) *logins.json and key3.db (decryption key) for Passwords saved in the Password Manager *cert8.db and possibly cert_override.txt for (intermediate) certificates stored in the Certificate Manager *persdict.dat for words you added to the spelling checker dictionary *permissions.sqlite for Permissions and possibly content-prefs.sqlite for other Site Preferences *sessionstore.js for open tabs and pinned tabs and tab groups *https://support.mozilla.org/kb/Recovering+important+data+from+an+old+profile *http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox