When I opened the forums this morning, I was already logged in, and it was http rather than https (as it has recently been).
I do not keep cookies, I do not store passwords; there’s nothing (to my knowledge) in my browser that would facilitate such an occurrence. Now I did have the issue occur yesterday afternoon (such as I’ve reported in this board) about the disappearing unread posts and browser freezing during the process. Thus I had to kill the browser; it prompted to restore the session this morning, but I choose to start a new session instead.
That’s normally what I do in that scenario, and I’ve never had this occur before.