I don't understand how this even helps... if the attacker (nene?) is the person who owns the computer, there is no way that "new private window" is somehow going to protect you.
If the attacker controls the computer, logging out won't help you either. First thing I'd do as an attacker is install a key logger to get the password. I assume that people who use shared computers don't have 2FA enabled.
I don’t really buy this. The tech kid in the village will explain that if abla doesn’t want nene to see her mail every time then abla should use the “new private window” button when she turns on the computer.
There’s no “basic human instinct” to be able to log into mail which this change goes against. Everyone had to be taught how to open the browser in the first place. The instructions have simply changed.