Tak mám to takto, včetně souboru jquery.ajax-cross-origin.min.js, který je ve stejném adresáři jako tento soubor.html a nic to nedělá...
<html>
<head>
  <script type="text/javascript" src="http://code.jquery.com/jquery-latest.min.js"></script>
  <script type="text/javascript" src="jquery.ajax-cross-origin.min.js"></script>
</head>
<body>
<select id="service">
  <option value="http://ip.jsontest.com/">IP Address</option>
  <option value="http://headers.jsontest.com/">HTTP Headers</option>
  <option value="http://date.jsontest.com/">Date & Time</option>
  <option value="http://echo.jsontest.com/key/value/one/two">Echo JSON</option>
  <option value='http://validate.jsontest.com/?json={"key":"value"};'>Validate</option>
  <option value="http://code.jsontest.com/">Arbitrary JS Code</option>
  <option value="http://cookie.jsontest.com/">Cookie</option>
  <option value="http://md5.jsontest.com/?text=[text%20to%20MD5]">MD5</option>
</select><br/>
<input type="text" id="url" style="width: 400px">
<input type="button" id="btn" value="Get JSON">
<br/><br/>
<div id="test" />
<script type="text/javascript">
$(function() {
  $( '#service' ).on( 'change', function(){
    $( '#url' ).val( $( this ).val() );
  });
  $( '#url' ).val( $( '#service' ).val() );
  $( '#btn' ).click(function(){
    var url = $( '#url' ).val()
    $.ajax({
      crossOrigin: true,
      url: url,
      success: function(data) {
        $( '#test' ).html(data);
      }
    });
  });
});
</script>
</body>
</html>