I have no sync key saved and can't get in without it
When I try to login to my sync account, under the Email address box and the password box is the notation "No saved Sync Key to use" therefor I cannot log in and I have found no way to add a sync key. I tried re-registering, but it won't let me because my email address is already being used. I am about to decide this service is not worth the hassle...
Sorry I missed this question... You can generate a new sync key for yourself. This will delete the info on the server and upload a new copy from your computer encrypted with the new sync key. https://support.mozilla.com/en-US/kb/Firefox%20Sync%20is%20not%20working#w_ive-lost-my-sync-key-what-can-i-do