This document summarizes Mario Heiderich's presentation titled "Locking the Throne Room - How ES5+ will change XSS and Client Side Security" given at BlueHat, Redmond 2011. The presentation discusses how new features in ECMAScript 5 (ES5), such as Object.defineProperty(), can be used to prevent cross-site scripting (XSS) attacks by locking down access to sensitive DOM properties and methods on the