gBrowser.tabContainer.addEventListener('load', function load(event) {
window.removeEventListener("load", load, false);
var urlString = 'http://stackoverflow.com/questions/';
if (gBrowser.currentURI.spec.startsWith(urlString)) {alert('ReadystateComplete')};
}, false);
gBrowser.tabContainer.addEventListener('TabSelect', function() {
var urlString = 'http://stackoverflow.com/questions/';
if (gBrowser.currentURI.spec.startsWith(urlString)) {alert('TabSelected')}