Disable online friend notification?

Is it possible to disable the notification that pop-ups everytime a user in my friend list gets online?

Yes, you can change your email notifications from the account setting page. On web (not available on iOS), click on your profile icon in the top right of the navigation and select the “account settings” page. - Joe @ NeonMob

Not the email notifications (that wouldn’t allow me to trade) I mean the little windows that pop-up in the upper left corner (in web) when a user that is in my friend list logs in.

Like this one

You cannot disable those pop ups, sorry. - Joe @ NeonMob