Notification when the value in Address Bar changes

How to get notified whenever the URL in the address bar (also known as location bar) changes. Using the following code, I tried to get notified when user navigates to another page (by clicking a link, using the back/forward button, by typing an address in the Location Bar, etc.) and also when user switches tabs.

var myExtension = {
oldURL: null,


init: function() {
    gBrowser.addProgressListener(this);
},

uninit: function() {
    gBrowser.removeProgressListener(this);
},

processNewURL: function(aURI) {
    if (aURI.spec == this.oldURL) return;

    // now we know the url is new...
    alert(aURI.spec);
    this.oldURL = aURI.spec;
},

// nsIWebProgressListener
QueryInterface: XPCOMUtils.generateQI(["nsIWebProgressListener",
                                       "nsISupportsWeakReference"]),

onLocationChange: function(aProgress, aRequest, aURI) {
    this.processNewURL(aURI);
},

onStateChange: function() {},
onProgressChange: function() {},
onStatusChange: function() {},
onSecurityChange: function() {}
};


};


window.addEventListener("load", function() { myExtension.init() }, false);
window.addEventListener("unload", function() { myExtension.uninit() }, false);

but this code is getting reference error for XPCOMUtils and window.I m developing this code on firefox Add-on Builder. Is there anything i need to import???

Solution

hey i got the answer of my question but with click event i need it work on page load event i tried document.addEventListener() but it didn't work

// This is an active module of the binitksingh (1) Add-on

    const contextMenu = require("context-menu"),
    data = require("self").data,
    notify = require("simple-notify").notify,
    tabs = require("tabs"),
    widgets = require("widget");


    exports.main = function(options, callbacks) {
   // Add a one-click option to addons bar.
    var widget = widgets.Widget({
    id: "Show-url",
    label: "Show URL",
    contentURL: "http://www.example.com/favicon.ico",


    onClick: function() {
        var tabworker = tabs.activeTab.attach({
            contentScriptFile: data.url('js/find-url.js'),
            onMessage: processUrl
        });
        tabworker.port.emit('click');
    },
});


 }


  function processUrl(url) {
    if (url) {
        notify("Hello now u r on:\n" + url);
             } else {
                notify('ZOMG, error finding URL.');
                    }
         }