I ended up at this page: https://badges.mozilla.org/en-US/browserid/browserid/verify/ – with a 403 message "CSRF verification failed. Request aborted."
My actions before: go to a badge claim page, logout, get redirected to home page, log back in (different email). In the end I seemed to have been logged in.
Successful attempt to reproduce: on home page log in, log out, log in again.
Hmm, I think logout is clearing the CSRF token from the session and breaking the hidden login form :/
I ran into the same thing today.. having something to do with using one persona email elsewhere and trying to log in to badges with a different one.
Ah whoops reported this here : https://bugzilla.mozilla.org/show_bug.cgi?id=1116529
Will try to keep an eye out for this issue, but I can't reproduce it. At least, not with various combinations of signing in places with persona. I have seen CSRF errors when memcache fails, though. But, that should hopefully be a transient infra issue