<!doctype html> <html> <head> <meta charset=utf-8> <script> Element.prototype.animate = function() { throw 'Called animate() as defined in content document'; } // Bug 1211783: Use KeyframeEffect (not KeyframeEffectReadOnly) here for (var obj of [KeyframeEffectReadOnly, Animation]) { obj = function() { throw 'Called overridden ' + String(obj) + ' constructor'; }; } </script> <body> <div id="target"></div> </body> </html>