You can define to load a page at a certain time of building DOM using run_at: for example with parameter page_start. this isn't working either. it seems to me that either the script is being run asynchronous, or there is some other reason for this not to be working: aall=document.getElementsByTagName("*"); for (var i=0, max=aall.length; i < max; i++) { aall.addEventListener=function(a,b,c){ console.log("Log"); return false; }; } console.log("Log"); is never being called, even though an event has been added to the element using addEventListener. My current solution for this is an own firefox fork that overwrites the functions in the javascript engine, which is kind of overdosed.