Shoutbox

If there were such a plugin, it could be terrible privacy invasion...so the answer is NO.

Whenever your contact opens/closes the conversation window, his Messenger sends a special notification to your Messenger. This is a Messenger's internal function, and the notification sends no matter StuffPlug is installed or not; StuffPlug just interprets the notification and shows it to you. When your contact is typing something to you, yes, Messenger does send another kind of notification too, but only the notification of "Typing message", not the whole message your contact's typing...