title: how to add the missing RANDR extension
body: <p>I have setup the xvfb server on my headless server and when I m running the
  DISPLAY=:99 firefox 
  I am getting this exception missing RANDR extension</p>
  
  <p>Many of them said to disable some xinerna from the xorg.conf file but this file is not getting created in my case.</p>
  
  <p>So I am searching for how to add the missing RANDR extension.</p>