[vladharbuz]

This should be no surprise — received chat messages are marked as read on Facebook if you wiggle your mouse after a few minutes of inactivity.

To be fair, this makes sense from a UX standpoint. You don't want messages to be marked as read if you have your window open but have walked away from the computer.

[proto-n]

This one is quite a big quality of life improvement IMO. It used to be that I sometimes left my browser accidentally open on facebook, and people would get offended because I 'read' their messages and didn't respond.

[jhowell]

Maybe telling your friends that you didn't actually see their message and that instead the algorithm FB uses to record my mouse activity sometimes reports that I have read messages that I have not. This sounds dangerous and could be harmful to a person's credibility if another with bad intentions acts.

[jhowell]

From a UI perspective it makes sense to persist my mouse activity to a database for eternity?