title: DOMMouseScroll event.wheelDelta is undefined on Firefox
body: <p>I am trying to add zooming to an SVG document but the DOMMouseScroll event.wheelDelta is undefined on Firefox. I have also tried using event.originalEvent.wheelDelta, this is also undefined. My code works in Chrome. This is the code I am using , any help would be appreciated.</p>
  
  <pre><code>var mousewheelevt=(/Firefox/i.test(navigator.userAgent))? "DOMMouseScroll" : "mousewheel" 
  
  if (theSvgElement.attachEvent)  
      theSvgElement.attachEvent("on"+mousewheelevt, zoomViaMouseWheel)
  else if (theSvgElement.addEventListener)  
      theSvgElement.addEventListener(mousewheelevt, zoomViaMouseWheel, false)
  
  function zoomViaMouseWheel(mouseWheelEvent) {  
      if(mouseWheelEvent.wheelDelta &gt; 0) {
          alert('scrolling up ! ' + mouseWheelEvent.wheelDelta);
      }
      else{
          alert('scrolling down ! ' + mouseWheelEvent.wheelDelta);
      }
  ...
  }
  </code></pre>