You have an existing Firefox profile from back in the firefox -P days but it does not show up under the fancy new "Manage profiles" item in the hamburger menu, and you'd like to fix that
- Create a new stub Profile using the "Manage profiles" mechanism; you can name it whatever you'd like since we only need Firefox to enregister it and create the new
Profilesdirectory - You can quit Firefox in that new Profile now
- ENSURE you do not have the old Profile in a running Firefox