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.
The Program ID is a unique identifier for your add-on. When you package your add-on for distribution using jpm xpi, it will become the ID field in the add-on's Install Manifest.
The ID is used for a variety of purposes. For example: addons.mozilla.org uses it to distinguish between new add-ons and updates to existing add-ons, and the simple-storage module uses it to figure out which stored data belongs to which add-on.
When you create an XPI with jpm xpi:
- if the package.json does not include an
idfield, then the ID written into the install.rdf is the value of thenamefield prepended with "@". - if the package.json does include an
idfield, and it contains "@", then this is written into the install.rdf as the add-on ID. - if the package.json does include an
idfield, and it does not contain "@", then jpm xpi raises an error and the XPI will not be built.