Firefox 38, wrong username or password

[3onyc]

I've tried to set up mozilla_sync with Firefox 38. I've followed the install document (Change settings, restart, sync -> create account).

Directly after this an "Incorrect account name or password" error pops up, I've checked the OwnCloud log and that contains a "No HTTP authentication header sent" entry.

However by checking tcpdump (And PHP's $_SERVER) it seems that the request it complains about indeed had no Authorization header (which rules out NGINX not passing it).

I see other requests in the tcpdump with the proper auth headers, so I don't know what's going on, any idea?

Version info:
OwnCloud: 8.0.3
NGINX: 1.4.6
uWSGI: 1.9.17.1
OS: Ubuntu 14.04