I tried logging into addons.mozilla.org after changing my Firefox account’s primary email address and it returned a JSON response saying “Internal Server Error”. When I change the email back to the previous primary, login works again. There is no extension or anything blocking the login and attempting to log in from Chrome yields the same results. I also tried revoking the login in the “Devices & Apps” section and logging in again, without success.
(This was originally posted on SUMO)