Unseenly for Facebook hides the seen feature in Facebook chat and Messenger. Your friends can't know when you read their message
Unseenly extension is for hiding the seen feature in Facebook chat. Currently this extension will work on www.facebook.com, m.facebook.com and messenger.com
All you have to do is just install the extension and you are good to go. You can easily toggle the extension ON and OFF by clicking the unseenly icon from your extensions list.
This is completely free, secure and free from malware and no unwanted pop-ups.