(this is copypaste from my another similar answer). You could try enabling "jQuery.support.cors=true" flag and see how it goes. I use jQuery v1.7.2.
I had to load webpage from local disk "file:///C:/test/htmlpage.html", call "http://localhost/getxml.php" url, and do this in IE8+ and Firefox12+ browsers, use jQuery v1.7.2 lib to minimize boilerplate code. After reading dozens of articles finally figured it out. Here is my summary.
- server script (.php, .jsp, ...) must return http response header Access-Control-Allow-Origin: *
- before using jQuery ajax set this flag in javascript:  jQuery.support.cors = true;
- you may set flag once or everytime before using jQuery ajax function
- now I can read .xml document in IE and Firefox. Other browsers I did not test.
- response document can be plain/text, xml, json or anything else
Here is an example jQuery ajax call with some debug sysouts.
jQuery.support.cors = true;
$.ajax({
    url: "http://localhost/getxml.php",
    data: { "id":"doc1", "rows":"100" },
    type: "GET",
    timeout: 30000,
    dataType: "text", // "xml", "json"
    success: function(data) {
        // show text reply as-is (debug)
        alert(data);
        // show xml field values (debug)
        //alert( $(data).find("title").text() );
        // loop JSON array (debug)
        //var str="";
        //$.each(data.items, function(i,item) {
        //  str += item.title + "\n";
        //});
        //alert(str);
    },
    error: function(jqXHR, textStatus, ex) {
        alert(textStatus + "," + ex + "," + jqXHR.responseText);
    }
});