by Andreas

Jquery + JSON: IE8/IE9 treats response as downloadable file

We’ve recently been working with the pretty brilliant web based elFinder file manager. This component has a truckload of features, but for a very specific function (uploading files through the web browser) we came across a tricky problem. Upon receiving a JSON response from an HTTP handler (.asxh) Internet Explorer 8 triggered the following warning:

To Help Protect Your Security, Internet Explorer has blocked this website from displaying content with security certificate errors. Click here for options…


After opting for “Download file”, subsequent responses just triggered the “Save file” dialog box. The contents of this file was the perfectly fine JSON response, but this was not understood by Internet Explorer 8. In Internet Explorer 9 the warning was supressed and the response seemed to simply be ignored, leaving our jQuery component waiting for its JSON reply in vain. Chrome, Opera and Firefox had no issues, and processed the response as pure JSON.

After a fair bit of research trying to find the bug both server and client side, it turned out that Internet Explorer didn’t like that the Content-Type in the response header was "application/json”. Setting the Content-Type to “text/html” specifically for IE in the .asxh handler before returning the JSON response did the trick. It now works as expected across all browsers.

A simple method checks the browser and updates the content type if applicable (note: this is just an extract):

        private static string SetContentTypeBasedOnBrowserAndCommand(HttpContext context)
            var contentType = "application/json"; // default
            // if browser is IE
            if (DegreeCore.Util.BrowserUtil.IsIE(context.Request.Browser))
                // override response
                 contentType = "text/html"; 

            return contentType;



The non-reversible hair loss from occational problems like this has yet again been put on hold – for now.

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