Intercepting Page Loads - Archive of obsolete content
here's a code sample that keeps track of your progress listeners for all tabs: init : function() { gbrowser.browsers.foreach(function (browser) { this._toggleprogresslistener(browser.webprogress, true); }, this); gbrowser.tabcontainer.addeventlistener("tabopen", this, false); gbrowser.tabcontainer.addeventlistener("tabclose", this, false); }, uninit : function() { gbrowser.browsers.foreach(function (browser) { this ._toggleprogresslistener(browser.webprogress, false); }, this); gbrowser.tabcontainer.removeeventlistener("tabopen", this, false); gbrowser.tabcontainer.removeeventlistener("tabclose", this, false); }, handleevent : function...
...(aevent) { let tab = aevent.target; let webprogress = gbrowser.getbrowserfortab(tab).webprogress; this._toggleprogresslistener(webprogress, ("tabopen" == aevent.type)); }, _toggleprogresslistener : function(awebprogress, aisadd) { if (aisadd) { awebprogress.addprogresslistener(this, awebprogress.notify_all); } else { awebprogress.removeprogresslistener(this); } } this shouldn't be too hard to follow.

tabs/utils - Archive of obsolete content
istabopen(tab) test whether the specified tab is open.

Session store API - Archive of obsolete content
in the latter case, a tabopen event is sent.

Tabbed browser - Archive of obsolete content
letabmoved(event) { var browser = gbrowser.getbrowserfortab(event.target); // browser is the xul element of the browser that's been moved } function exampletabremoved(event) { var browser = gbrowser.getbrowserfortab(event.target); // browser is the xul element of the browser that's been removed } // during initialization var container = gbrowser.tabcontainer; container.addeventlistener("tabopen", exampletabadded, false); container.addeventlistener("tabmove", exampletabmoved, false); container.addeventlistener("tabclose", exampletabremoved, false); // when no longer needed container.removeeventlistener("tabopen", exampletabadded, false); container.removeeventlistener("tabmove", exampletabmoved, false); container.removeeventlistener("tabclose", exampletabremoved, false); note: startin...

Event reference
tabopen addons specific a tab has been opened.