There is no option to turn it off with Facebook UI. The extension was previously available at, you can find a couple of alternatives in the store by searching for them. To not risk any more trouble with Facebook, I will not provide an instruction on how to install extensions manually and will also not continue developing it. Since it was developed open source and the source is available at GitHub, I updated the link to point to the GitHub Page. Update: Facebook requested me to take the extension down since it violates their Terms of Services.

One drawback of this extension is that all your messages will be marked as unread for yourself, too, and the 'unread messages' notification stays visible as long as you do not reply (or explicitly mark it as read). But with 'FB unseen' you can 'Mark as read' whatever you want, so you can decide for yourself when the 'Seen' flag is set.

If you want you can use any adblocker to achieve this. The only thing you need to do is block the URL:į/ajax/mercury/change_read_status.phpįor Chrome, use the extension 'FB unseen' which blocks the URL (full disclosure: I wrote this extension).

Disable facebook messenger