Why does VEMap onclick event work in other browsers but not Firefox?

I've got a VEMap control with the following relevant bits of code:

map = new VEMap('map');

map.AttachEvent("onclick", DoContinents);

function DoContinents(event)
     {
        if (event.elementID != null)
        {
        //var shape = map.GetShapeByID(event.elementID);
        //var id = shape.GetID();
        //var id = event.elementID;
        //alert (event.elementID);
        if (event.elementID == 'msftve_1001_200000_10000')
            {
                map.SetCenterAndZoom(new VELatLong(15, -90), 2);
        }
          else if (event.elementID == 'msftve_1001_200001_10001')
            {
                map.SetCenterAndZoom(new VELatLong(48, 23), 2);
            }
             else if (event.elementID == 'msftve_1001_200002_10002')
            {
            map.SetCenterAndZoom(new VELatLong(4, 18), 2);
                }
             else if (event.elementID == 'msftve_1001_200003_10003')
            {
                map.SetCenterAndZoom(new VELatLong(43, 87), 2);
                }
            else if (event.elementID == 'msftve_1001_200004_10004')
            {
                map.SetCenterAndZoom(new VELatLong(-25, 134), 2);
                }

            cont.Hide();
            vid.Show();
            $('#sidebar_list').show();
            $('#legend').show();
        }
     }

It works just fine in Chrome, and even in IE! However when I load the page in Firefox nothing happens when I click on my map icons. Upon further investigation I discovered that the event fires in all browsers and DoContinents runs. In Chrome and IE, event.elementID contains the ID of the VEShape I clicked but in Firefox event.elementID is null (even though there is an event object)! Obviously this causes the code in my DoContinents event handler not to run. Why would this happen in Firefox but not my other browsers?

This was a hard one to track down but it turns out if the following conditions are met, VEMap events break. They still fire but critical event data such as elementID is missing.

1. Only happens in Firefox
2. When the mootools JS framework is being loaded (not necessarily being used)

When these conditions are met the aforementioned problem occurs.

Be aware that Joomla automatically loads mootools. This is what happened to me.