I tried to login on a (new) Firefox browser (to SO), and went through the authentication, and it says 'Welcome Jonathan Leffler', and then leaves me in the intro screen (the 'no user' screen).
I opened this Meta page; it recognized me OK. I opened a SO page from my already logged in page on a Chrome browser on the same machine and it doesn't recognize me. So I have one tab in Chrome logged in as me, but another tab in the same Chrome not logged in. And the Firefox on the same machine is having problems.
SO Version 2013.5.22.696.
Anyone else seeing anything similar?
(I use a slightly odd MyOpenID login; I don't know if that affects this.)