MDN’s new design is in Beta! A sneak peek: https://blog.mozilla.org/opendesign/mdns-new-design-beta/

High-Level APIs

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.

From Firefox 53 onwards, no new legacy add-ons will be accepted on addons.mozilla.org (AMO).

From Firefox 57 onwards, WebExtensions will be the only supported extension type, and Firefox will not load other types.

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 WebExtensions if they can. See the "Compatibility Milestones" document for more.

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

Modules listed on this page implement high-level APIs for building add-ons: creating user interfaces, interacting with the web, and interacting with the browser.

Unless the documentation explicitly says otherwise, all these modules are "Stable": we'll avoid making incompatible changes to them.

addon-page
Create a page that does not contain navigational elements.
base64
Data encoding and decoding using Base64 algorithms.
clipboard
Interact with the system clipboard, setting and getting its contents.
context-menu
Adds items, submenus, and menu separators to the page's context menu.
hotkeys
Assign hotkey combinations to functions in your add-on.
indexed-db
Exposes the IndexedDB API to add-ons.
l10n
Localize strings appearing in the add-on's JavaScript code.
notifications
Display transient, toaster-style desktop messages to the user.
page-mod
Run scripts in the context of web pages whose URL matches a given pattern.
page-worker
Create a permanent, invisible page and access its DOM.
panel
Creates transient dialogs to implement part of an add-on's user interface.
passwords
Interact with Firefox's Password Manager to add, retrieve and remove stored credentials.
private-browsing
Check whether a given object is private, so an add-on can respect private browsing
querystring
Utility functions for working with query strings.
request
Make simple network requests.
selection
Get and set text and HTML selections in the current web page.
self
Access data that is bundled with the add-on, and add-on metadata.
simple-prefs
Store preferences across application restarts.
simple-storage
Lets an add-on store data so that it's retained across Firefox restarts.
system
Query the add-on's environment and access arguments passed to it.
tabs
Open, manipulate, and access tabs, and receive tab events.
timers
Set one-off and periodic timers.
ui
Provides access to button, toolbar, and sidebar UI objects.
url
Construct, validate, and parse URLs.
webextension
Provides functions for communicating with an embedded WebExtension.
widget
Create a simple user interface for an add-on in Firefox's add-on bar.
windows
Enumerate and examine open browser windows, open new windows, and listen for window events.

Document Tags and Contributors

Tags: 
 Contributors to this page: wbamberg, DavidWalsh
 Last updated by: wbamberg,