Facebook recently added some features to its Messages, Chat and Groups that a lot of people have found to be somewhat sketchy.
In Groups, anyone with permission to view a post can hover over it and see a list of other people who have read it. This could actually be functional if you're using it to coordinate meeting times or sharing documents for work. But when it comes to Messages and Chat, it gets a little creepy. Not only will people always know if you've read a message or not, "you’ll now see the name of town or city from which a message was sent in-line if your conversation partners have location enabled."
If you don't want your Facebook Messenger to have a built-in white lie detector, try Chat Undetected. It's a browser extension that works across Chrome, Firefox, Internet Explorer and Safari. All you have to do is install it and it disables read receipts so you can stay incognito when you want to be.
This extension is made by Crossride.com