Internet Explorer 11 for Windows 8.1 introduced SPDY support to IE for the first time. Unfortunately, it doesn't work properly if your browser is configured to use a proxy server, so you'll need to disable it if you want sites that support SPDY to load properly.
See http://angrytechnician.wordpress.com/2014/01/16/google-not-loading-first-time-in-ie11-via-a-web-proxy-on-windows-8-1-turn-off-spdy-support/ for the full details.
