If you don't have access to the original email account that the Firefox Account was created with, then you will need to make a new account under your new email address. If you are concerned about your old data staying on the Mozilla servers, you can use the ''Forgot your password'' feature to reset your password on your old account. Even if you can't access the old email address to change the password, your data is wiped from the account when you request a new password. If you have access to the old account (or are signed into Sync on another browser), you can add your new email address as a secondary email address to your existing account. Once you confirm that email address, you will be able to set it as your primary email address and remove your old email address from the account. Hope this helps.