Sometime back Facebook introduced a new ‘Seen’ feature that simply notifies its users when their private message or chat is seen by the receiver. You can easily disable Facebook ‘Seen’ notification option from there if you are a Google Chrome user.
All you will be needing to do is install FB unseen extension in your chrome web-browser and that’s all. Now your friends will never get notified when you see their private messages and chats.
But the extension has one drawbag, all your messages will get marked as read for yourself too, and “unread messages” notification stays visible until you send a reply.