Javascript callback function throws error "Callback is not a function" in firefox
<pre><code>function CascadeDropDowns(parentClass, childClass, action, callback) {
  var DropDownId = $(parentClass + " option:selected").val();

  $.ajax({
    url: "/site/" + action,
    data: { DropDownId: DropDownId },
    dataType: "json",
    type: "POST",
    error: function () {
      alert("An error occurred.");
    },
    success: function (data) {
      var items = "";
      $.each(data, function (i, item) {
        items += "&lt;option value=\"" + item.Value + "\"&gt;" + item.Text + "&lt;/option&gt;";
      });
      $(childClass).html(items);
      $(childClass)[0].selectedIndex = 0;
      callback();
    }
  });
}

$(document).ready(function () {
  // Populates all child drop downs on load
  var callback = function () {
    CascadeDropDowns(".ConfigGroupDDL", ".ConfigNameDDL", "GetParameters");
  };

  CascadeDropDowns(".DeviceTypeDDL", ".ConfigGroupDDL", "GetGroups", callback);

  // Populates all child drop downs parent change
  $(".DeviceTypeDDL").change(function () {
    var callback = function () {
      CascadeDropDowns(".ConfigGroupDDL", ".ConfigNameDDL", "GetParameters");
    };
    CascadeDropDowns(".DeviceTypeDDL", ".ConfigGroupDDL", "GetGroups", callback);
  });
  $(".ConfigGroupDDL").change(function () {
    CascadeDropDowns(".ConfigGroupDDL", ".ConfigNameDDL", "GetParameters");
  });
});
</code></pre>

<p>This runs fine and cascades the dropdowns in the right order, but firefox debugger shows an error and ie throws an alert and asks if Id liek to debug. </p>

<p>Any advice would be great</p>
