Hm, I see I made a mistake. That's what I usually suddenly realize right after asking for help. I suppose JCF, in contrast to J2O, doesn't actually use cookies for logging in and out. I'm not sure why I was unable to log in with my phone, which I'm almost sure can store cookies, but the privacy settings of the browser on the PC make it impossible to store them (it's not mine, so I didn't know that and I won't change it to check if I'm right - but I have to be right). I wonder why does J2O need cookies to stay logged in, but I expect there's no serious reason to change it. Sorry for the false alarm.