1. Login with your Facebook account.
2. If you are using Google Chrome browser, just press F12 function key. If you are Firefox user, then press Ctrl + Shift + K to open inspect element window.
3. Switch to Console section.
4. Click here to get script. Copy the entire code and paste into text box of Console section.
5. Hit Enter. Type any message you would like to send to all friends such as "Happy New Year" , "Happy Cristmas" etc. Click on "Post".
Note: Use this script once in a day else Facebook will temporary block your messaging service for doing bulk messaging.