If you made a typo in the email address of a Firefox Account then you won't be able to confirm this account and nothing will be uploaded to the Sync server, so if this email address would belong to someone else then they wont be able to access your data. Just create a new account with the correct email address, so you can confirm this account via the email that will be send to this email address. See also: *https://support.mozilla.org/en-US/kb/ive-lost-my-firefox-sync-account-information