What account are you talking about? For a normal user account on the forums, open your profile and correct the information. You should also change the password. If you are talking about sync, Resetting the sync password, or changing its e-mail, will remove all data from the servers. This is a security feature. https://support.mozilla.org/en-US/kb/ive-lost-my-firefox-sync-account-information *I've lost my Firefox Sync account information - What to do *I’ve forgotten, or don't have access to, my Firefox Account email address