The ‘seen’ feature in Facebook is quite useful as it lets you know when your message has been read by your friend. It turns out to be a life saver sometimes when you want a time sensitive message to be delivered.
However this feature is also used by friends to know you are simply ignoring them or you are really away from Facebook. The feature forces you to reply to the person in a guilt that your friends might feel you are not giving importance to them.
Disabling this seen feature may come to your mind at times, fortunately there are ways to do that and read all the Facebook Messages without notifying your friends.
Install this Privy Chat for Facebook, it is just like the Facebook Messenger for Android but doesn’t notify your friends that their messages has been seen by you. The feature is disabled just in this Privy Chat for Facebook app and if you check the messages from Facebook app or Facebook Messenger app, your friend will be notified with a ‘seen’ icon.
Disable ‘seen’ feature on PC
Install this Chrome extension FB unseen. It blocks the ‘seen’ feature from Facebook chat. You can turn off/on the extension anytime. The “unread messages” notification stays visible as long as you do not reply (or mark it explicit as read.)