I am new to Firefox Extension Development and doing my 1st program. Simply I needed to pop up a alert once it loaded the page. My code was like this:

var myExtension = {  
init: function() {    
    if(gBrowser) gBrowser.addEventListener("DOMContentLoaded", this.onPageLoad, false);  
},  
onPageLoad: function(aEvent) { 
alert("Loaded");  
}
}  
window.addEventListener("load", function load(event){  
window.removeEventListener("load", load, false);
myExtension.init();    
},false); 

But I am getting the alert box for couple of times. Then I found about "#document" and then I added a IF condition:

onPageLoad: function(aEvent) { 
    if (aEvent.originalTarget.nodeName == '#document')  {
    alert("Loaded");  
    }
}

Unfortunately still I am getting the same. Please advise me on this.