var tabs = require("sdk/tabs");

   tabs.on("open",openTab);
   tabs.on("ready",readyTab);
   tabs.on("close",closeTab);

 if (!isBrowser(domWindow) || ignoreWindow(domWindow))
   return;

 let window = null;
 try {
   modelFor(domWindow);
 }
 catch (e) { }

 for (let tabElement of getTabs(domWindow)) {
   addWindowTab(window, tabElement);
 }

I am developing a Firefox add-on using Add-on SDK tool. I am doing something as soon as a tab is opened. I registered for all tab's event( open,ready,close). var tabs = require("sdk/tabs"); tabs.on("open",openTab); tabs.on("ready",readyTab); tabs.on("close",closeTab); And i have respective functions for each event Listener. Problem which i am facing is some of the webpages opened in a new window. For those web pages none of the event Listener is firing. Please help me out in this. By debugging the following function at resource://gre/modules/commonjs/sdk/tabs/tabs-firefox.js // Detect tabs in new windows windowObserver.on('open', domWindow => { if (!isBrowser(domWindow) || ignoreWindow(domWindow)) return; let window = null; try { modelFor(domWindow); } catch (e) { } for (let tabElement of getTabs(domWindow)) { addWindowTab(window, tabElement); } }); When I go to the page "http://www.yourhtmlsource.com/javascript/popupwindows.html", then go to the line "Try it here: » Pop it" and lick on "Pop it", a new popup window appeared, and I found that the function isBrowser(domWindow) always returns FALSE with the popup window. Please help me the way to make addon SDK make isBrowser(domWindow) return TRUE.