title: read "about config" prefrences of mozilla firefox using javascript
body: <p>I want to know that how can I read the <code>about:config</code> preferences of Mozilla Firefox ? Please note that I do not want to change its value, I only want to read them.</p>
  
  <p>I've already gone through 
  <a href="https://stackoverflow.com/questions/3796084/about-config-preferences-and-js">about-config-preferences-and-js</a></p>
  
  <p>but  I end up following error.
  <code>RefrenceError: getPrefs is not defined</code>.</p>
  
  <p>Will anyone help to get me out from this?</p>