const Cu = Components.utils; function run_test() { var sb = new Cu.Sandbox('http://www.example.com'); let w = Cu.evalInSandbox('var w = new WeakMap(); w.__proto__ = new Set(); w.foopy = 12; w', sb); do_check_eq(Object.getPrototypeOf(w), sb.Object.prototype); do_check_eq(Object.getOwnPropertyNames(w).length, 0); do_check_eq(w.wrappedJSObject.foopy, 12); do_check_eq(w.foopy, undefined); }