As Linux 64 build 20181021220134, GitHub can't be used with login. When logging into GitHub, I see the logged-in state of the first page that loads after login. Thereafter, trying to load anything that does not require login shows the not-logged-in state. Anything that requires login redirects to https://github.com/session, which says the browser did something unexpected. The value of network.cookie.cookieBehavior does not seem to affect this. Marking as blocker, since this prevents getting work that requires GitHub done.

Hmm. Broken on release channel, too. Might be breakage on the GitHub side: https://status.github.com/messages

This was a problem at GitHub's end.