DOMNodeInserted is known to make dynamic pages slow, MDN even recommends not using it altogether, but doesn't provide any alternatives.
I'm not interested in the element inserted, I just need to know when some script modifies the DOM. Is there a better alternative to mutation event listeners (maybe getElementsByTagName inside an nsiTimer)?
One new alternative that @naugtur briefly mentioned is MutationObserver. It's designed as a replacement for the deprecated mutation events, if the browser(s) you're developing for supports it (like if you're developing a browser extension).
If all you want to do is trigger an event when the DOM changes, do something like this:
var nodes=document.getElementsByTagName('*')||document.all;
function domchange(){
alert('Hello');
}
window.setInterval(function(){
var newnodes=document.getElementsByTagName('*')||document.all;
if(newnodes!=nodes){
nodes=newnodes;
domchange();
}
},1);