title: event is undefined for firefox browser on calling oncontextmenu
body: <p>I am displaying context menu on right-clicking a button in a page. The code used for displaying context menu is </p>
  
  <pre><code>window.addEventListener('contextmenu',function (e){e.preventDefault();},false);}
  </code></pre>
  
  <p>When I am right clicking the button, the context menu method called is </p>
  
  <pre><code>displaycontextmenu(obj,event)
  {
        console.log("Context");
        console.log(event);
        // Displaying context menu
  }
  </code></pre>
  
  <p>The code executes fine in IE browser, even in chrome I can  see in console that "<strong>Context</strong>" and event is printed. But in firefox , it is printing as "<strong>Context</strong>" and <strong>undefined</strong>.
  I am really confused to see here that the event is undefined. </p>
  
  <p>I am using the event to get the x and y co-ordinates to display the context menu at right place. Since the event is undefined, am not able to proceed further.</p>