I created a new VS 2013 project and viewed the default.aspx page with the Firefox browser. When I check the net calls it has made, I see it making constant calls to:
Had issues with that on site running with KnockoutJS framework. Pages were freezing for 10 seconds until "BrowserLink" external scripts were loading (using Chrome browser).
Issue solved by disabling "Browser link" feature in VS 2013
Steps How to disable "Browser link" (thanks to Gustavo Armenta for leaving comment with link in question)