gistfile1.js

function load() {

	var prefix = 'http://tw.dt.in.th/thaiWitter/';
	if (window.location.href.substr(0, prefix.length) == prefix) {
		// do some required work here
	}

	var mediator = Components.classes["@mozilla.org/appshell/window-mediator;1"]
		.getService(Components.interfaces.nsIWindowMediator);
	var windows = mediator.getEnumerator(null);
	while (windows.hasMoreElements()) {
		var currentWindow = windows.getNext();
		if (currentWindow.location.href == 'chrome://webrunner/content/webrunner.xul') {
			var browser = currentWindow.document.getElementById('browser_content');
			if (browser.contentWindow.wrappedJSObject == window) {
				currentWindow.WebRunner._firstLoad = true;
			}
		}
	}

}