Why are the websites detecting my phone as Windows 7?

[Windows Central Question]

After installing the Insider's Preview, my web experience certainly ruined, an old version of Google opens, also YouTube videos wont work, it says to install an app to play them. When I visited windowsphone.com it says "Know more about your Windows 7" (Although I am running on Windows 10 TP) . Is it one of the problem with the Preview? Please answer. Thanks