Corresponds to fx-sync bug 571897: If you change your sync password while another client is still connected, the next sync on that client will produce "unknown error" rather than a helpful login failure notice.
(In reply to comment #0) > Corresponds to fx-sync bug 571897: Copy'n'paste FAIL. Meant to say bug 584486
Created attachment 465906 [details] [diff] [review] v1 Port the fix from bug 584486. NB: I'm away for a week starting tomorrow, so someone else will have to land or address review comments if people feel this needs to land urgently.