Thunderbird WebExtension APIs

Thunderbird WebExtensions are very similar to those of Firefox. These documents assume you have some familiarity with building a WebExtension for Firefox. If not, it is highly recommended to begin by reading some of the MDN documentation on the subject.

WebExtension APIs are asynchronous, that is, they return a Promise object which resolves when ready. See Using Promises for more information about Promises.

The documents were generated automatically from the schema documents at mail/components/extensions/schemas.


This documentation is for pre-release versions of Thunderbird. See the “78” version for Thunderbird 78, or the “68” version for Thunderbird 68. For any problems or feature requests please file a bug.


In Thunderbird, all WebExtension API can be accessed through the browser.* namespace, as with Firefox, but also through the messenger.* namespace, which is a better fit for Thunderbird.

The following APIs are also included and work as they do in Firefox:

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