jQuery在Chrome和Safari中工作，但不能在Firefox或IE中工作

我被一些JavaScript/jQuery代码所难倒，这些代码在Webkit浏览器（Chrome和Safari）中完美运行，但在Firefox或IE中根本无法工作，我希望有人可以指出我的错误？

我正在做的是使用jQuery提取GeoRSS提要，然后使用Leaflet在地图上绘制位置点。不知何故，使用火狐或IE时没有绘制点？这是有问题的页面：http://bit.ly/19N0I75

这是代码：

var map = L.mapbox.map('map', 'primitive.geography-class').setView([42, 22], 4);
var wordpressIcon = L.icon({
iconUrl: 'http://www.shifting-sands.com/wp-content/themes/shiftingsands/images/icons/wordpress.png',
iconSize:     [18, 18], // size of the icon
shadowSize:   [0, 0], // size of the shadow
iconAnchor:   [9, 9], // point of the icon which will correspond to marker's location
shadowAnchor: [0, 0],  // the same for the shadow
popupAnchor:  [0, 0] // point from which the popup should open relative to the iconAnchor
});
jQuery(document).ready(function($){
$.get("http://shifting-sands.com/feed/", function (data) {
var $xml = $(data);
var $i = 0;
$xml.find("item").each(function () {
    var $this = $(this),
        item = {
            title: $this.find("title").text(),
            linkurl: $this.find("link").text(),
            description: $this.find("description").text(),
            pubDate: $this.find("pubDate").text(),
            latitude: $this.find("lat").text(),
            longitude: $this.find("long").text()
        }
                lat = item.latitude;
                long = item.longitude;
                title = item.title;
                clickurl = item.linkurl;
                //Get the url for the image.
                var htmlString = '<h4><a href="' + clickurl + '" target="_blank">' + title + '</a></h4>';                       
                var contentString = '<div id="content">' + htmlString + '</div>';   
                //Create a new marker position using the Leaflet API.
                var rssmarker = L.marker([lat, long], {icon: wordpressIcon}).addTo(map);
                //Create a new info window using the Google Maps API
                rssmarker.bindPopup(contentString, {closeButton: true});

    $i++;
});
});
});

谢谢！