Something

  $('#facebox form#send_mail').live('submit', function(event){
    var $form = $(this);
    $.ajax({
      url: $form.attr('action'),
      type: 'POST',
      data: $form.serialize(),
      dataType: 'json',
      complete: function(response) {
        if (response.statusText == 'parsererror') { // no valid JSON returned, this is HTML to inject
          $form.html(response.responseText);
        }
      },
      success: function(response) {
        $.facebox.close();
        $('#notification').html($('<ul class="' + response.type + '"><li>' + response.message + '</li></ul>'));
      }
    });
    event.preventDefault();
  });