<system.webServer> <staticContent> <mimeMap fileExtension=".json" mimeType="text/html" /> </staticContent> </system.webServer>
to my web.config in an Azure instance worked just fine. Most likely, your deployed web.config isn't configured properly. To check it out, enable RDP, connect to your Azure instance and browse to your web.config. Then you can fiddle with your web.config until you get things working.
Because you're serving up a static .json file, you don't need to add a .json HTTP handler. Also, the offical mime type for .json is application/json.