I was registering for an add-on account and mistyped my email address. Now I cannot log in to my user name because I cannot click on the registration email sent to the incorrect address.
(Please update to Firefox 18.0.1, the version you are running is horribly out of data Update Firefox to the latest version )
Why don't you just create another account and use the correct address?
You can't change the email, so delete that wrongly created sync account and create a new account: