How “seen” feature works in Chat box :- When you open facebook on your browser their is an AJAX script that is running continuously  behind the browser. This script can read the time you have read the message and send seen notification to your friend.

# For Chrome Browser

Download Chrome Plugin To disable the seen feature in facebook chat This Plugin Blocks the ”seen” feature of the facebook messenger. After installing plugin you can set whether to turn on or turn off that feature in facebook.

# For Mozilla Firefox Browser

Download BlockSite plus plugin for Firefox Addons Then go to tools > options > extensions. Click the options button in Blocksite plus and paste in below URL and select quick add.

www.facebook.com/ajax/mercury/change_read_status.php

If you have any difficulty then please comment below, If I can then I will surely Help You.]]>