The reason for this problem is: In the folder at C:\Users\&lt;username&gt;\AppData\Roaming\Mozilla\F

The reason for this problem is:

In the folder at

C:\Users\<username>\AppData\Roaming\Mozilla\Firefox

there are two .ini files which Firefox uses as an index to locate your profile folders. When you remove the default profile folder, Firefox complains about not being able to find it because it is still listed as default in those files (installs.ini, profiles.ini).

What you need to do now

Use a plain text editor to change the profile paths in installs.ini and profiles.ini from the deleted folder to the one you put back into the Profiles folder.

What does that look like -- hypothetical paths in installs.ini

BEFORE (matches the removed folder):

Default=Profiles/abcd1234.default-release-345713438241

AFTER (matches the current folder):

Default=Profiles/7654zwxy.default-release

Do you see what I did there?