Firefox Extension: Add a button to the navigation toolbar

gistfile1.js

// Source: http://stackoverflow.com/questions/5572632/firefox-how-can-i-add-modify-toolbars-using-the-add-on-sdk-jetpack
// Only works on first window opened..

var data = require("self").data;
var {Cc, Ci} = require("chrome");
var mediator = Cc['@mozilla.org/appshell/window-mediator;1'].getService(Ci.nsIWindowMediator);

exports.main = function(options, callbacks) {
    addToolbarButton();
    // other stuff
};

function addToolbarButton() {
    var document = mediator.getMostRecentWindow("navigator:browser").document;      
    var navBar = document.getElementById("nav-bar");
    if (!navBar) {
        return;
    }
    var btn = document.createElement("toolbarbutton");  

    btn.setAttribute('type', 'button');
    btn.setAttribute('class', 'toolbarbutton-1');
    btn.setAttribute('image', data.url('img/icon16.png')); // path is relative to data folder
    btn.setAttribute('orient', 'horizontal');
    btn.setAttribute('label', 'My App');
    btn.addEventListener('click', function() {
        // use tabs.activeTab.attach() to execute scripts in the context of the browser tab
        console.log('clicked');
    }, false)
    navBar.appendChild(btn);
}