I want to run the scripts in Headless mode for all the 3 browsers Chrome, Firefox & IE
The following is the code for Chrome:
System.setPropert
IE does not have support for a headless mode (since IE nowadays does not recieve any kind of update or improvements.).
But you can use trifle.js, a kind of browser that can emulate some IE versions in a headless mode, since its coded as a port of PhantomJS.