I'm logged into several SE sites and in the past chat did worked for me. However since some time it refuses to log me in stating I'm not logged on any SE site. I've tried both with Fx and WebKit Epiphany.
There is no problem with tavern.
Edit: After logging out everywhere and logging in on SE site pressing log in in chat it says that my data auth is too old as oppose to previous behavior of logging indefinitly.
Global auth stopped working about the same time.