I just want to know if is correct ti let you know about it ?

Hi!

It's fine to keep using the old email that you don't no longer user. The email address acts as a username (and to recover a lost password).

In any case, if you wan to use your new address, you can do so by creating a new account with it. At this moment, is not possible to change the email address on the Firefox Sync account.

Best, Ibai