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


BrowserApp.addTab() opens a new tab. By default, the new tab is made the selected tab.


var tab = window.BrowserApp.addTab(uri);

var tab = window.BrowserApp.addTab(uri, params);

The URI to load into the tab, represented as a string.
An optional parameter which contains any of these properties:
  • pinned: boolean property, true if you want the new tab to be pinned as an app tab. Defaults to false.
  • selected: boolean property, true if you want the new tab to be made the selected tab. Defaults to true.
  • isPrivate : boolean property, true if you want the new tab to be opened in private browsing mode. [This editor's note: in my tests, defaulted to false]


tab: the new tab, represented as a Tab object.


This code implements a simple "View Source" add-on, using BrowserApp.addTab() to open a new tab displaying the current tab's source:

function viewSource(window) {
  window.BrowserApp.addTab("view-source:" + window.content.location.href);

var menuId;

function loadIntoWindow(window) {
  if (!window)
  menuId ="View Source", null, function() {

function unloadFromWindow(window) {
  if (!window)

This function opens the specified uri in a new tab, without selecting the tab:

function openUnselected(window, uri) {
  let params = {
    selected: false
  window.BrowserApp.addTab(uri, params);

See Also

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Last updated by: rebloor,