Boot-additions.scala

    // In cases where we have an AJAX request for IE with an uploaded file, we
    // assume we served through an iframe (a fairly safe assumption) and serve
    // up the response with a content type of text/plain so that IE does not
    // attempt to save the file.
    LiftRules.responseTransformers.append {
      resp =>
        (for (req <- S.request) yield {
          resp match {
            case InMemoryResponse(data, headers, cookies, code)
                                    if ! req.uploadedFiles.isEmpty &&
                                        req.isIE &&
                                        req.path.wholePath.head == LiftRules.ajaxPath =>
              InMemoryResponse(data, ("Content-Type", "text/plain; charset=utf-8") :: headers, cookies, code)
            case _ => resp
          }
        }) openOr resp
    }

lift-iframe-upload.js

$(document).load(function() {
  var iframe =
    $('<iframe name="upload-iframe" />')
      .css('display', 'none')
      .load(function() {
          $.globalEval($(this).contents().text());
          setupForm();
        });
  $('body').append(iframe);

  function setupForm() {
    $('#form-wrapper form')
      .attr('target', 'upload-iframe')
      .removeAttr('onsubmit')
      .attr('action', '/ajax_request/' + lift_page)
      .attr('method', 'post')
      .attr('encoding', 'multipart/form-data')
      .attr('enctype', 'multipart/form-data')
      .find('input:submit, button[type=submit]')
        .removeAttr('onclick')
      .end()
      .append($('<input type="hidden" name="' +
                  $('#form-wrapper form').find('input:submit, button[type=submit]').attr('name') +
                  '" value="_" />'))
      });

  setupForm();
});