Fix file upload in IE

lms/djangoapps/django_comment_client/base/views.py

 import functools
 import logging
+import json
 import random
 import time
 import urlparse
@@ -7,7 +8,7 @@ import urlparse
 from django.contrib.auth.decorators import login_required
 from django.contrib.auth.models import User
 from django.core import exceptions
-from django.http import Http404, HttpResponseBadRequest
+from django.http import Http404, HttpResponseBadRequest, HttpResponse
 from django.utils.translation import ugettext as _
 from django.views.decorators import csrf
 from django.views.decorators.http import require_GET, require_POST
@@ -750,13 +751,16 @@ def upload(request, course_id):  # ajax upload file to a question or answer
         result = ''
         file_url = ''
 
-    return JsonResponse({
+    # Using content-type of text/plain here instead of JSON because
+    # IE doesn't know how to handle the JSON response and prompts the
+    # user to save the JSON as a file instead of passing it to the callback.
+    return HttpResponse(json.dumps({
         'result': {
             'msg': result,
             'error': error,
             'file_url': file_url,
         }
-    })
+    }), content_type="text/plain")
 
 
 @require_GET