The other thing to be aware of, is that when logging in, there is a little box (for a check mark) that says, "Remember Me"
If that isn't toggled, when you log in, then your "session" times out in 20 minutes, if you haven't done anything in the forum. This forces you to log in again.
The other thing this option does is to auto log you in, if you leave TFL and come back at a later time. You still get auto-logged out after 20 minutes of no activity, but you also get auto-logged in when you return.
Hope this helps.