Do you still have access to that email address? If so, you can reset the Firefox Account password to obsolete any data in the account. Because the data was encrypted with a key that contains the old password, it won't be recoverable. But I don't know whether it will actually be deleted. See: I've lost my Firefox Sync account information - What to do.

You also can submit a request through OneTrust using a form linked at the bottom of the privacy policy:

https://www.mozilla.org/privacy/

The link is labeled "See here for Data Subject Access Requests".

I don't know what kind of verification process is involved with those requests.

Do you still have access to that email address? If so, you can reset the Firefox Account password to obsolete any data in the account. Because the data was encrypted with a key that contains the old password, it won't be recoverable. But I don't know whether it will actually be deleted. See: I've lost my Firefox Sync account information - What to do. You also can submit a request through OneTrust using a form linked at the bottom of the privacy policy: https://www.mozilla.org/privacy/ The link is labeled "See here for Data Subject Access Requests". I don't know what kind of verification process is involved with those requests.

This password resetting gimmick doesn't work for the mere fact that they retain my email address. Since I am locked out of the account, I have no reason to believe that any other personal information was purged. Retaining encrypted data is unacceptable.

I have submitted the request through that OneTrust form.