For FireFox Users
- Download the BlockSite plus plugin from here : Firefox Addons
- Then go to tools > options > extensions.
- Click the options button in BlockSite plus and paste in below URL and select quick add.
Everytime you open your browser just add this and you are done.Now your friends will not know when you have read their message
For Chrome Users
- You can simply download the below add on and install it . Plugin Download Link
- After installing it you can set whether to turn on or turn off that feature in Facebook.