Seen & Typing Blocker for Facebook
Now you can make sure people you are chatting with on Facebook (and Messenger) cannot see whether you read or have "✓ Seen" their message. They also won't be able to see if you're typing. Simply install this extension. You'll see the monkey covering his eyes emoji in your toolbar. If you click it, the monkey will change to the normal monkey emoji. This means people can now see if you read their message, and see if you're typing. You can go back and forth between this behavior. Note: once you reply to a message, obviously previous messages are marked as read.