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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 (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.

Add-on types hold useful information about each type of add-on that may be installed. They are mostly used to help the UI know how to display the different types of add-on.


Attribute Type Description
id string The unique ID for the type.
name string The localized name for the type.
uiPriority integer

A number used to determine the order of types displayed in the user interface. The lower the number the higher in the list the type will appear.

Built-in Values:

Value Category
2000 Locale
4000 Extension
5000 Theme
6000 Plugin
viewType integer The type of UI to use to display this type of add-on in the UI. If undefined the type will not appear in the UI.
flags integer Additional behavior flags for the type.

Document Tags and Contributors

 Contributors to this page: bunnybooboo, Leif-AMO, Sheppy, arantius, erikvold, clokep, Mossop
 Last updated by: bunnybooboo,