This it not Mafia Wars related, but more stalker related…. if you hate people knowing when you have seen/ read their messages, here is a BM or userscript i wrote that will let you peek at the message without them knowing you have read/seen it…

Expand your facebook messages

bookmark -> FB ExpandIt

Bookmark Version

Drag the bookmark above to your bookmark bar.
Run/click the bookmark when you are on your facebook message page
It will insert a Expand It+ link next to available messages.
Click Expand It+ and this will let you read the message without telling the user that you have read it.

Userscript/Chrome Version

This will put a Expandit!+ link to all your messages without having to run the BM.

Chrome Install

Firefox Install