Remove the ”seen” feature from the facebook messenger. Your friends won´t be able to tell if you read their messages.
UNSEEN FOR FACEBOOK AND MORE
Blocks the ”seen” feature of Facebook Messenger, on both facebook.com and messenger.com. Blocks referer during surfing.
Unseen removes the "seen at" notification from Facebook and Facebook Messenger. Install the extension and remain your privacy. None of your friends will see that you have read their messages.