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

Source: Thunderbird WebExtension APIs — Thunderbird WebExtension APIs documentation