I found this page that has details on tabbed browsing in firefox including the event handlers to be notified when the selected tab is changed: http://developer-stage.mozilla.org/en/docs/Code_snippets:Tabbed_browser --Senwtoiv 20:48, 28 November 2007 (EST)

URL CHANGE: http://developer.mozilla.org/en/docs/nsIWebProgressListener#onStateChange --Senwtoiv 20:57, 7 February 2008 (EST) http://developer.mozilla.org/en/docs/Code_snippets:Progress_Listeners