Cannot remove locales from the locale alternatives list

Steps to reproduce

Tested in 12.5.2:

1. Go to "Language" in "about:preferences".
2. Click "Set Alternatives...".
3. Add a language to the list.

Result

No way to remove the added language from the alternatives list because the "Remove" button is disabled. The only option is to move it up and down.

Expect

Be able to remove locales from the list.

I think this is a limitation may be coming from firefox to not allow the user to removing packaged locales.