DateFormat.js

renderer: function (value) {
    if (value) {
        var millis = value;
        var year = new Date(millis).getFullYear();
        var month = new Date(millis).getMonth();
        var day = new Date(millis).getUTCDate();
        return Ext.util.Format.date(new Date(year, month, day, 0, 0, 0), 'm-d-Y');
    }

    return null;
}