Historical Overview

The architecture of Thunderbird extensions has changed over the years. The following table describes the different legacy extension types.

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.

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": "myextension@sample.extensions.thunderbird.net",
      "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

pageUpdate for Thunderbird 78pageAdapt to Changes in Thunderbird 69-78

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