Hi, unfortunately that is not going to happen. You were suppose to change your address before. After does not work due to the Security of the User Account. Firefox Support Volunteers do not have access to your information. Nor does anyone else other than you.

Too late now, but you should have added a secondary email address before you lost access to that "sold" domain. That would have allowed you to keep using that Firefox Account with the secondary email address.

What happened to bring about the need to access your Firefox Account? The data sitting in your Sync account should still be on all your devices that are / were connected to that Sync Account. Unless all your devices were lost or were formatted at the same time, your data should still be on at least one device. In that case all you need to do is to create a new Firefox Account on that one device and thus get your data to the Sync server into that new Firefox Account; then connect the other devices one at a time to have them all connected to Sync.