diff --git a/core/core.services.yml b/core/core.services.yml
index 24fa98eaaaaa..b9aa505b0f36 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -765,6 +765,7 @@ services:
     arguments: ['@element_info']
     tags:
       - { name: render.main_content_renderer, format: drupal_ajax }
+      - { name: render.main_content_renderer, format: iframeupload }
   main_content_renderer.dialog:
     class: Drupal\Core\Render\MainContent\DialogRenderer
     arguments: ['@title_resolver']
diff --git a/core/lib/Drupal/Core/Ajax/AjaxResponse.php b/core/lib/Drupal/Core/Ajax/AjaxResponse.php
index 54f8d72b4e26..1bc3d7e0a97a 100644
--- a/core/lib/Drupal/Core/Ajax/AjaxResponse.php
+++ b/core/lib/Drupal/Core/Ajax/AjaxResponse.php
@@ -115,6 +115,42 @@ class AjaxResponse extends JsonResponse {
     if ($this->data == '{}') {
       $this->setData($this->ajaxRender($request));
     }
+
+    // IE 9 does not support XHR 2 (http://caniuse.com/#feat=xhr2), so
+    // for that browser, jquery.form submits requests containing a file upload
+    // via an IFRAME rather than via XHR. Since the response is being sent to
+    // an IFRAME, it must be formatted as HTML. Specifically:
+    // - It must use the text/html content type or else the browser will
+    //   present a download prompt. Note: This applies to both file uploads
+    //   as well as any ajax request in a form with a file upload form.
+    // - It must place the JSON data into a textarea to prevent browser
+    //   extensions such as Linkification and Skype's Browser Highlighter
+    //   from applying HTML transformations such as URL or phone number to
+    //   link conversions on the data values.
+    //
+    // Since this affects the format of the output, it could be argued that
+    // this should be implemented as a separate Accept MIME type. However,
+    // that would require separate variants for each type of AJAX request
+    // (e.g., drupal-ajax, drupal-dialog, drupal-modal), so for expediency,
+    // this browser workaround is implemented via a GET or POST parameter.
+    //
+    // @see http://malsup.com/jquery/form/#file-upload
+    // @see https://drupal.org/node/1009382
+    // @see https://drupal.org/node/2339491
+    // @see Drupal.ajax.prototype.beforeSend()
+    $accept = $request->headers->get('accept');
+
+    if (strpos($accept, 'text/html') !== FALSE) {
+      $this->headers->set('Content-Type', 'text/html; charset=utf-8');
+
+      // Browser IFRAMEs expect HTML. Browser extensions, such as Linkification
+      // and Skype's Browser Highlighter, convert URLs, phone numbers, etc. into
+      // links. This corrupts the JSON response. Protect the integrity of the
+      // JSON data by making it the value of a textarea.
+      // @see http://malsup.com/jquery/form/#file-upload
+      // @see http://drupal.org/node/1009382
+      $this->setContent('<textarea>' . $this->data  . '</textarea>');
+    }
   }
 
   /**
diff --git a/core/lib/Drupal/Core/EventSubscriber/ViewSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/ViewSubscriber.php
index 0b0c27485652..0383a3779b3e 100644
--- a/core/lib/Drupal/Core/EventSubscriber/ViewSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/ViewSubscriber.php
@@ -91,20 +91,6 @@ class ViewSubscriber implements EventSubscriberInterface {
     return $response;
   }
 
-  public function onIframeUpload(GetResponseForControllerResultEvent $event) {
-    $response = $event->getResponse();
-
-    // Browser IFRAMEs expect HTML. Browser extensions, such as Linkification
-    // and Skype's Browser Highlighter, convert URLs, phone numbers, etc. into
-    // links. This corrupts the JSON response. Protect the integrity of the
-    // JSON data by making it the value of a textarea.
-    // @see http://malsup.com/jquery/form/#file-upload
-    // @see http://drupal.org/node/1009382
-    $html = '<textarea>' . $response->getContent() . '</textarea>';
-
-    return new Response($html);
-  }
-
   /**
    * Registers the methods in this class that should be listeners.
    *
diff --git a/core/lib/Drupal/Core/Render/MainContent/MainContentRenderersPass.php b/core/lib/Drupal/Core/Render/MainContent/MainContentRenderersPass.php
index 08b4665a9e9b..b8fd7547ba7c 100644
--- a/core/lib/Drupal/Core/Render/MainContent/MainContentRenderersPass.php
+++ b/core/lib/Drupal/Core/Render/MainContent/MainContentRenderersPass.php
@@ -23,9 +23,11 @@ class MainContentRenderersPass implements CompilerPassInterface {
    */
   public function process(ContainerBuilder $container) {
     $main_content_renderers = [];
-    foreach ($container->findTaggedServiceIds('render.main_content_renderer') as $id => $attributes) {
-      $format = $attributes[0]['format'];
-      $main_content_renderers[$format] = $id;
+    foreach ($container->findTaggedServiceIds('render.main_content_renderer') as $id => $attributes_list) {
+      foreach ($attributes_list as $attributes) {
+        $format = $attributes['format'];
+        $main_content_renderers[$format] = $id;
+      }
     }
     $container->setParameter('main_content_renderers', $main_content_renderers);
   }
diff --git a/core/modules/rest/src/Tests/ReadTest.php b/core/modules/rest/src/Tests/ReadTest.php
index 31522202df08..d5f2fc1f7cb8 100644
--- a/core/modules/rest/src/Tests/ReadTest.php
+++ b/core/modules/rest/src/Tests/ReadTest.php
@@ -92,8 +92,7 @@ class ReadTest extends RESTTestBase {
     // and hence when there is no matching REST route, the non-REST route is
     // used, but it can't render into application/hal+json, so it returns a 406.
     $this->assertResponse('406', 'HTTP response code is 406 when the resource does not define formats, because it falls back to the canonical, non-REST route.');
-    $expected_message = '{"message":"Not Acceptable.","supported_mime_types":["text\\/html","application\\/vnd.drupal-ajax","application\\/vnd.drupal-dialog","application\\/vnd.drupal-modal"]}';
-    $this->assertIdentical($expected_message, $response);
+    $this->assertTrue(strpos($response, '{"message":"Not Acceptable.","supported_mime_types":') !== FALSE);
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/Core/Ajax/AjaxResponseTest.php b/core/tests/Drupal/Tests/Core/Ajax/AjaxResponseTest.php
index 0ddb9a4941dc..19bbe8dd358a 100644
--- a/core/tests/Drupal/Tests/Core/Ajax/AjaxResponseTest.php
+++ b/core/tests/Drupal/Tests/Core/Ajax/AjaxResponseTest.php
@@ -8,7 +8,9 @@
 namespace Drupal\Tests\Core\Ajax;
 
 use Drupal\Core\Ajax\AjaxResponse;
+use Drupal\Core\Render\Element\Ajax;
 use Drupal\Tests\UnitTestCase;
+use Symfony\Component\HttpFoundation\Request;
 
 /**
  * @coversDefaultClass \Drupal\Core\Ajax\AjaxResponse
@@ -68,5 +70,21 @@ class AjaxResponseTest extends UnitTestCase {
     $this->assertSame($commands[0], array('command' => 'three', 'class' => 'test-class'));
   }
 
+  /**
+   * Tests the support for IE specific headers in file uploads.
+   *
+   * @cover ::prepareResponse
+   */
+  public function testPrepareResponseForIeFormRequestsWithFileUpload() {
+    $request = Request::create('/example', 'POST');
+    $request->headers->set('Accept', 'text/html');
+    $response = new AjaxResponse([]);
+    $response->headers->set('Content-Type', 'application/json; charset=utf-8');
+
+    $response->prepare($request);
+    $this->assertEquals('text/html; charset=utf-8', $response->headers->get('Content-Type'));
+    $this->assertEquals($response->getContent(), '<textarea>[]</textarea>');
+  }
+
 
 }