Hi, sorry I am not much help, I am looking to find the solution for same problem too. All I can tell, that you can keep your old email to log into sync, but I have a new device and it's not allowing me now to sign in, as it only wants to send confirmation email to the old email, which they have already closed down long long time ago... I had this problem once already, when I had to contact somebody from Firefox, who helped me through this trouble.. I am trying to find the way now AGAIN with the same problem... Here we go, so many years passed, still no solution. I could add another email, which I can use, but they do not send confirmation email to that one... ridiculous.. I am hoping for a change.. and that I can find the way as I was finding it years before too, to get somebody actually helping me to log into my account, which still hold old old email where I do not get no confirmation email for long time..

Thanks for reaching out. If I find a solution at some point, I'll let you know.

Glad to know I am not crazy or alone in this struggle. If I find a solution at any point, I'll reach out. Thank you.

HI. I don't know if this actually helps you or not: https://support.mozilla.org/en-US/kb/change-primary-email-address-firefox-accounts I have found this useful for my problem, I had to add a third email address and they were sending me the confirmation email to there - so I could log in (the new device is still not syncing though... i read others had same problem..) however, when I added the email, it didn't allow me to make it primary, like in this article. there is even a picture of it, nonsense... Thought to share it with you, anyway.

Thank you!