Thunderbird provides the following messenger related WebExtension APIs, which are sometimes referred to as MailExtension APIs.
Enables an extension to access information of accounts and identities configured in Thunderbird's account manager.
Enables an extension to access, modify, create and delete Thunderbird address books.
Enables an extension to interact with a browser action button.
Enables an extension to register a cloudFile provider, which can be used to upload large attachments to a server, instead of attaching them directly to the email.
The commands API adds keyboard shortcuts that can trigger actions in an extension. Permission info:
Enables an extension to open a new message compose window or react to events while the message is being composed.
Enables an extension to interact with a compose action button.
Functionally is the same as the contentScripts API except that it works on the document of email messages during composition.
Enables an extension to access, modify, create and delete contacts in Thunderbird address books.
Enables an extension to access, modify, create and delete mail account folders.
Enables an extension to access, modify, create and delete mailing lists in Thunderbird address books.
Enables an extension to interact with Thunderbird's main window. Permission info:
Enables an extension to add (context-) menu entries to Thunderbird menus. Permission info:
Enables an extension to react on and interact with the currently displayed messages.
Enables an extension to interact with a message display action button. Permission info:
Functionally is the same as the contentScripts API except that it works on the document of email messages being displayed.
Enables an extension to list, search, read, copy, move and delete messages.
tabs, activeTab, compose, messageModify
Enables an extension to interact with Thunderbird's tab system. It allows to create, modify, and rearrange tabs and to communicate with scripts in tabs. Permission info:
The theme API can be used to create static or dynamic Thunderbird themes. Theme experiments are supported.
Enables an extension to interact with Thunderbird's windows which can contain webpage tabs and also other window types like composer or address books that cannot contain webpage tabs. You can use this API to create, modify, and rearrange windows.
You can find more information in the Thunderbird WebExtensions API documentation .
As Thunderbird is based on Firefox, many of its WebExtension APIs can be used in Thunderbird as well. The APIs listed in the following table are known to work with Thunderbird.
Enables an extension to modify certain global browser settings. Because these are global settings, it's possible for extensions to conflict. See the documentation for
Enables an extension to copy items to the system clipboard. Currently the API only supports copying images, but it's intended to support copying text and HTML in the future. Permission info:
Use this API to register content scripts to instruct the browser to insert the given content scripts into pages that match the URL patterns specified during registration. In Thunderbird, content scripts can only be used in web pages loaded into tabs. Permission info:
Enables an extension to get and set cookies, and be notified when they change. Permission info:
Enables an extension to resolve domain names.
Enables extensions to interact with the browser's download manager. You can use this API to save files to disk. Permission info:
Utilities related to an extension. Gets URLs to resources packages with an extension. Gets the
Functions to internationalize an extension. It can be used to get localized strings from locale files packaged with an extension and to find out Thunderbird's current language.
Use the identity API to get an OAuth2 authorization code or access token, which an extension can then use to access user data from a service that supports OAuth2 access (such as Google or Facebook).
Find out when the user's system is idle, locked, or active.
Access and modify various privacy-related settings.
Gets information about installed add-ons. Permission info:
Display notifications to the user, using the underlying operating system's notification mechanism.
Enables extensions to request extra permissions at runtime, after they have been installed.
Enables an extension to enumerate PKCS #11 security modules and to make them accessible as sources of keys and certificates.
Enables an extension to proxy web requests. Use the
This module provides information about the extension and the environment it's running in. It also provides messaging APIs to:
Enables extensions to store and retrieve data, and listen for changes to stored items.
Use this API to register user scripts, third-party scripts designed to manipulate webpages or provide new features. Registering a user script instructs the browser to attach the script to pages that match the URL patterns specified during registration. In Thunderbird, user scripts can only be used in web pages loaded into tabs. This API offers similar capabilities to contentScripts but with features suited to handling third-party scripts.
Add event listeners for the various stages of a navigation. A navigation consists of a frame in the browser transitioning from one URL to another, usually (but not always) in response to a user action like clicking a link.
Add event listeners for the various stages of making an HTTP request, which includes websocket requests on
You can find more information about these APIs in the MDN WebExtension API documentation.