<html> <body> Aloha! My URL is <span id='url'></span>. <script> document.getElementById('url').innerHTML = window.location; </script> <script> // The input element is getting synthesized key events and will prevent // default on the first ESC keydown event. var alreadyBlocked = false; addEventListener('keydown', function(e) { if (e.keyCode == SpecialPowers.Ci.nsIDOMKeyEvent.DOM_VK_ESCAPE && alreadyBlocked == false) { alreadyBlocked = true; e.preventDefault(); } }); </script> </body> </html>