How to convert legacy extensions?

The architecture of Thunderbird extensions has changed over the years. The following table describes the different legacy extension types, and how they can be converted to modern WebExtensions.

The current Thunderbird ESR no longer supports legacy extensions.

If you are currently maintaining a legacy extension, please identify the type of your extension in the table below and check the provided guides on updating your extension to remain compatible with the latest versions of Thunderbird.

Wrapped WebExtension

Status: Unsupported in Thunderbird 128.

Wrapped WebExtension are modern WebExtensions, which use a so-called wrapper Experiment (the WindowListener Experiment or the BootstrapLoader Experiment). These Experiments were provided as an intermediate solution after legacy WebExtensions had been deprecated in Thunderbird 78. After 4 years, the Thunderbird team is no longer able to maintain the two mentioned wrapper Experiments and developers should no longer use them.

Wrapped WebExtensions have a background script similar to the following:

await messenger.WindowListener.registerDefaultPrefs(
    "defaults/preferences/prefs.js"
);
await messenger.WindowListener.registerChromeUrl([
    ["content",  "myaddon",          "chrome/content/"],
    ["resource", "myaddon",          "chrome/"],
    ["locale",   "myaddon", "en-US", "chrome/locale/en-US/"],
    ["locale",   "myaddon", "de-DE", "chrome/locale/de-DE/"],
]);
await messenger.WindowListener.registerOptionsPage(
    "chrome://myaddon/content/options.xhtml"
);
await messenger.WindowListener.registerWindow(
    "chrome://messenger/content/messengercompose/messengercompose.xhtml",
    "chrome://myaddon/content/messengercompose.js"
);
await messenger.WindowListener.startListening();

Update Strategy

Convert wrapped WebExtensions to modern WebExtensions

Legacy WebExtension

Status: Deprecated in Thunderbird 78.

Legacy WebExtensions are legacy overlay extensions or legacy bootstrap extensions wrapped inside a WebExtension.

They use a JSON manifest (manifest.json) with the legacy key (which has been deprecated in Thunderbird 78):

{
  "manifest_version": 2,
  "applications": {
    "gecko": {
      "id": "[e-mail]",
      "strict_min_version": "68.0"
    }
  },
  "name": "Extension",
  "description": "Does a thing",
  "version": "2.0",
  "icons": {
    "32": "content/icon32x32.png"
  },
  "legacy": {
    "type" : "bootstrap",
    "options": {
      "page": "chrome://myextension/content/options.xul",
      "open_in_tab": true
    }
  }
}

Update Strategy

Convert legacy WebExtensions to modern WebExtensions

Adapt to Changes in Thunderbird 69-78

Legacy Bootstrap Extension

Status: Deprecated in Thunderbird 68.

This type of extension uses a bootstrap file (bootstrap.js) as an entry point to the extension. The file defines four methods (install, uninstall, startup, and shutdown) from which all extension behaviour is controlled. These extensions can be installed/uninstalled and enabled/disabled without restarting Thunderbird, so they are sometimes called "restartless" extensions. They use an RDF manifest (install.rdf).

Update Strategy

It is recommended to update legacy bootstrap extensions to legacy WebExtensions first, before converting them to modern WebExtension. The update guide assumes, the extension is currently compatible with Thunderbird 60. If that is not the case, you can find further update instructions here.

Convert legacy bootstrapped extension to legacy WebExtension

Adapt to Changes in Thunderbird 61-68

Legacy Overlay Extension

Status: Deprecated in Thunderbird 68.

The original type of extension for Thunderbird and Firefox, using documents that overlay the Thunderbird UI, adding to and modifying it. These extensions use an RDF manifest (install.rdf) and require a restart of Thunderbird for installation/uninstallation, upgrading/downgrading and enabling/disabling.

Update Strategy

It is recommended to update legacy overlay extensions to legacy WebExtensions first, before converting them to modern WebExtensions. The update guide assumes, the extension is currently compatible with Thunderbird 60. If that is not the case, you can find further update instructions here.

Convert legacy overlay extension to legacy WebExtension

Adapt to Changes in Thunderbird 61-68