Support for extensions using XUL/XPCOM or the Add-on SDK was removed in Firefox 57, released November 2017. As there is no supported version of Firefox enabling these technologies, this page will be removed by December 2020.

Add-ons using the techniques described in this document are considered a legacy technology in Firefox. Don't use these techniques to develop new add-ons. Use WebExtensions instead. If you maintain an add-on which uses the techniques described here, consider migrating it to use WebExtensions.

Starting from Firefox 53, no new legacy add-ons will be accepted on (AMO) for desktop Firefox and Firefox for Android.

Starting from Firefox 57, only extensions developed using WebExtensions APIs will be supported on Desktop Firefox and Firefox for Android.

Even before Firefox 57, changes coming up in the Firefox platform will break many legacy extensions. These changes include multiprocess Firefox (e10s), sandboxing, and multiple content processes. Legacy extensions that are affected by these changes should migrate to use WebExtensions APIs if they can. See the "Compatibility Milestones" document for more information.

A wiki page containing resources, migration paths, office hours, and more, is available to help developers transition to the new technologies.


The Tab object is only available to privileged code running on Firefox for Android, and is intended for use by Firefox for Android add-ons.


The Tab object represents a browser tab, and provides access to the browser and the DOM content window hosted by that tab.

You access Tab objects from the BrowserApp object. BrowserApp provides access to all tabs through its tabs property, and to the currently selected tab through its selectedTab property.


An identifier for this tab.
The XUL browser object hosted by this tab.
The DOM content window hosted by this tab.


This function retrieves the array of open tabs from BrowserApp, then fetches each tab's DOM content window, and logs the title of the DOM document loaded into the window:

function logTabTitles(window) {
  var tabs = window.BrowserApp.tabs;
  tabs.forEach(function(tab) {

This function retrieves the selected tab, then retrieves its browser property, which it uses to log the current tab's session history:

function logSelectedTabHistory(window) {
  var tab = window.BrowserApp.selectedTab;
  var enumerator = tab.browser.sessionHistory.SHistoryEnumerator;
  while (enumerator.hasMoreElements()) {
    var historyEntry = enumerator.getNext().QueryInterface(Components.interfaces.nsIHistoryEntry);

If you want to retrieve the selected tab's URL, use this code:

var url = window.BrowserApp.selectedTab.browser.currentURI.spec;

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Last updated by: rebloor,