You can check compatibility.ini in this profile folder to see what Firefox version/path last used this profile. Primary location used for the main profile that keeps your personal data (Root Directory on about:profiles). *C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile> *https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data *https://support.mozilla.org/en-US/kb/dedicated-profiles-firefox-installation