Well, this is new and doesn't at all smell like finger printing

For context: I'm already logged in on my phone (and this PC has logged into FB before also). So, how does that work, exactly? Log out, try to log in from phone...same issue, as now BOTH devices are logged out?

Hmm. Near as I can tell, this is due to clearing cookies recently / history. Having said that, I've cleared cookies thousands of times before and been able to log in just fine. Which therefore suggests...what.. policy change server-side, not a coincidence? I'm on the same hardware, same browser, same IP. FB appears to have changed what counts as "trusted."

PS: Yeah, I hate FB too. It's the only way I have to communicate with some folks. Believe me, given the option, I'd make em all use Signal or XMPP.