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 addons.mozilla.org (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.
There are a couple of differences between desktop Firefox and Firefox for Android that are particularly relevant to add-on developers:
- there is no visible XUL in the user interface, so you can't use XUL overlays to create your add-on's UI
gBrowserobject does not exist, so you can't use
tabbrowserto interact with browser tabs
Instead, Firefox for Android provides its own APIs:
NativeWindowenables you to manipulate parts of the native Android UI
BrowserAppenables you to interact with browser tabs
- PageActions.jsm allows you to add buttons to the urlbar.
Prompt.jsmallows you to easily show native prompts, dialogs, menus, and lists
Notifications.jsmallows you to handle system notifcations
Home.jsmallows you to customize the home page
HomeProvider.jsmallows you to store data to show on the home page
Accounts.jsmallows you to start the Firefox Account set-up process
Snackbars.jsmallows you to show Snackbar notification.
In these pages we've documented the main functions and properties exposed by these objects. To see all the details, refer to the code at
We also have some modules that don't ship with Firefox for Android but can be used in addons:
Sound.jsmlets you play sounds in the browser simply