I have the following AJAX JSONP request, to a third-party free webservice (success and error actions simplified):

      $.ajax({
          type: 'get',
          url: 'http://openapi.ro/api/companies/123456789.json',
          dataType: 'jsonp',     
          success: function(data) {
              alert(data.name);
          },
          error: function(data) {
              alert('fail')
          }
                   
      });

If the call fails (404 for instance), the error callback is not invoked in Firefox 11. In Chrome, Safari (Windows) and IE9 the callback is invoked properly.

Also, in the Firebug tools, the 404 response is visible.

To workaround this, the 'timeout' parameter needs to be added. With the timer parameter present, the error callback is fired normally, after the timeout has elapsed

The behaviour has always been reproduced under Firefox 11 (several computers as well) with the above AJAX request