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

Legacy Bootstrap Extension

Legacy Overlay Extension