Cannot create a new Firefox account using my original email address.

I previously had a Firefox account registered with my original email address. Recently, I changed the account’s primary email by adding a secondary email address, switching it to become the primary email, and then removing the secondary email address. After completing this change, I attempted to create a new Firefox account using the original email address that was previously associated with my account. However, during the sign-up process, I receive the error message: "Primary account email required for sign-in." It appears that the original email address may still be linked to the previous account in some way, preventing it from being used to register a new account. I would like to understand why this is happening and how I can free the email address so it can be used to create a new Firefox account.