Firefox Bootstrapped Add-On Injecting before load - firefox

Question

Is it possible to add event listeners for a document before a page has been navigated to using a Bootstrapped add-on? I would like to see what page the user wants to navigate to as well as later after the page loads to inspect the DOM. I need to run code in the HTML content context.
In the past I used a toolbar XUL and included javascript within it and it would load before the HTML page loaded.

Answer 1

i looked into doing stuff before DOMContentLoaded sometime ago and found out there is a document inserted observer.
order of events after running research code at bottom
readystate changes to interactive (i think multiple times, not sure)
readystate changes to complete
DOMContentLoaded event fires
load event fires (Sometimes load doesnt fire, if you might have to change addEventListener with capture arugment (3rd argument) as false or true)
apparently there should be readystate loading before all of this but i can never catch it i dont know why.
after running the code in scratchpad, browser environemnt of course, then load a new page and watch the error console it will throw these reports in this order:
ready state changed! ("interactive") Scratchpad/4:18
02:28:07.873 ready state changed! ("complete") Scratchpad/4:18
02:28:07.874 DOMContentLoaded event fired! Scratchpad/4:53
02:28:07.938 Load event fired! Scratchpad/4:45
here is the research code. it adds a the listeners and observer to see whats firing.
var {classes: Cc, interfaces: Ci, utils: Cu} = Components;
var os = Cc['#mozilla.org/observer-service;1'].getService(Ci.nsIObserverService);
var LMObserver;
function myObserver() {
this.register();
}
myObserver.prototype = {
observe: function (subject, topic, data) {
//Cu.reportError(subject);
//Cu.reportError(data);
//i think subject is window element
subject.onreadystatechange = function () {
//loading
//interactive
//complete
Cu.reportError('ready state changed! ("' + subject.readyState + '")');
//var body = subject.documentElement.querySelector('body')
//you want to change title so you would do that here do something like: if (subject.readystate == 'complete') { subject.title = 'blah blah' }
//Cu.reportError('has body element: ' + body)
}
},
register: function () {
os.addObserver(this, 'document-element-inserted', false);
},
unregister: function () {
os.removeObserver(this, 'document-element-inserted', false);
}
};
//below this is the DOMContentLoaded thing i put this here so we can see what fires in what order
var pageLoad = function(event) {
var win = event.originalTarget.defaultView;
if (win && win.frameElement) {
return;
}
Cu.reportError('Load event fired!');
}
var pageDOMContentLoaded = function(event) {
var win = event.originalTarget.defaultView;
if (win && win.frameElement) {
return;
}
Cu.reportError('DOMContentLoaded event fired!');
}
LMObserver = new myObserver;
gBrowser.addEventListener("load", pageLoad, true);
gBrowser.addEventListener("DOMContentLoaded", pageDOMContentLoaded, true);
//gBrowser.removeEventListener("load", pageLoad, true);
//gBrowser.removeEventListener("DOMContentLoaded", pageDOMContentLoaded, true);
//LMObserver.unregister();
Here's some more indepth research on load events added with true or false as capture argument: https://github.com/Noitidart/event-listener-experiment-DOMC-and-load/blob/master/bootstrap.js