jquery ajax does not work in Firefox

jquery ajax does not work in Firefox

Help!

I am using jquery ajax to retrieve data from an asp.net web service.  It works ok in IE8; but when I tried it on Firefox (3.6 or so), it generated an error:  parsererror

So much for cross-platform transparency.

Here is server code snipet:

            JavaScriptSerializer js = new JavaScriptSerializer();
            string strJSON = js.Serialize(rows);
            return strJSON;


Here is the jquery code:

    function CallService() {   
        $.ajax({
            type: "POST",
            url: "http://localhost:49405/AjaxWS.asmx/GetExternalSoftwareList",
            data: "{}",
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            success: OnSuccess,
            error: OnError
        });
    }
    function OnSuccess(data, status) {

       var  c = eval("(" + data.d + ")");
    }
    function OnError(request, status, error) {
        alert(status);
    }


Thanks for helping!