Unfortunately, FiOS does not offer a Windows 10 app that is compatible with the Xbox One. You may be able to watch live TV on your computer through Google Chrome or Microsoft Edge by following these instructions:
1) Go to http://xfinity.com/ and enter in your Username and Password into the login box at the top of the page
2) Click Sign In near bottom right hand corner
3) Open up Internet Explorer browser and type in xfinitytv.com using URL bar