title: jquery popup window position firefox issue
body: <p>I have a jquery popup window script on my site. It works fine in chrome but in firefox when the window is opened, it appears right at the top, where I want it to appear vertically more centered. Eg.</p>
  
  <pre><code> ________________________
  |     |           |     |
  |     |   popup   |     |
  |     |           |     |
  |     |___________|     |
  |                       |
  |_______________________|
  </code></pre>
  
  <p>The script in popup.js:</p>
  
  <pre><code>function centerPopup(){
    var windowWidth = document.documentElement.clientWidth;
    var windowHeight = document.documentElement.clientHeight;
    var windowTop =window.screenTop;
    var popupHeight = $(".popupContent").height();
    var popupWidth = $(".popupContent").width();
  
    $(".popupContent").css({
      "position": "fixed",
      "top": (windowTop+250)-popupHeight/2,
      "left": windowWidth/2-popupWidth/2
      });
  
    //this is needed for ie6
    $(".backgroundPopup").css({ "position": "fixed", "height": windowHeight, "top": windowTop });
    }
  </code></pre>
  
  <p>Can anyone offer any suggestions what I need to change to get it working correct?</p>
  
  <h2>UPDATE</h2>
  
  <p>The code above is from the popup.js script, there's also a popup.css, im not sure if anything in this part of it is conflicting or causing a problem</p>
  
  <pre><code>   .popupContent{
  display:none;
  align: center;
  position: fixed;
  _position: fixed; 
  height:auto;
  width:500px;
  background:#fff;
  z-index:9999;
  padding:8px;
  -moz-border-radius: 10px;
  -webkit-border-radius: 5px;
  -khtml-border-radius: 5px;
  border-radius: 5px;
  background-color: #15150B;
  border:2px solid #C9C58F;
  }
  </code></pre>