Hiding "last online" and "seen" on Facebook messenger
I find that seeing when a user was last online and whether he has read a message contributes to toxic behavior.
This is invasive to the other persons private life and will basically incite the users to spy on each others, making them come back to this page without purpose.
I don't know if you consider this falls within the scope of this add-on, but if you want to test it, the CSS rules would be the following
._3eus {
display: none;
}
._2v6o {
display: none;
}
._2her._9ah {
display: none;
}