Well I was searching view json file in WebBrowser in my Desktop app, when I try in IE still same problem IE was also prompt to download the file. Luckily after too much search I find the solution for it.
You need to : Open Notepad and paste the following:
[HKEY_CLASSES_ROOT\MIME\Database\Content Type\application/json] "CLSID"="{25336920-03F9-11cf-8FD0-00AA00686F13}" "Encoding"=hex:08,00,00,00Save document as Json.reg and then right click on file and run as administrator.
After this You can view json file in IE and you Desktop WebBrowser enjoy :)