Whenever you receive a message on Facebook and read it, a notification appears in the sender's chat box that you have seen the message.

A similar extension that is also available for Google Chrome is Facebook Chat Privacy.

It blocks any "seen" and "is typing" status messages. It is available for Firefox, Opera and Chrome and can be used to customize Facebook.

One of the features that it offers is to block read receipts on the site.

The Google Chrome extension Facesnoop works out of the box.

Just install it and it is enabled right away when you are on Facebook.

Note that this only affects Facebook in Chrome with the extension installed.

If you access Facebook in another way, for instance on your mobile, read receipts are still sent.

Facesnoop is a new browser extension for Google Chrome that blocks "seen" notifications on Facebook.

While you can still read all messages like before that y0u receive, senders don't receive a read notification anymore when you do so.