i think that happens because of cookies, if they're cleared you get logged out. do you have settings on firefox that do that? i don't use it so can't tell you.
Try it on Firefox. Plenty of things don't happen on Chrome because that's all devs test. That and Safari iOS.
Which does make things less of an evil intent and more of a "if our laziness pushes our users to where we make money, that's an unfortunate side effect".
