Supported UI Elements

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Descriptions and examples of MailExtension APIs to interact with Thunderbird's user interface.
Browser Action
A browser action adds a button to Thunderbird's main toolbar:
It is controlled by the browser_action manifest key in the extension's manifest.json file:
"browser_action": {
    "default_title": "Restart",
    "default_icon" : "restart.png",
    "default_popup": "browser_popup.html"
},
If a default_popup is defined, a popup will be opened and the defined html page will be loaded, when the button is clicked. Additionally, you can use the browserAction API in your background script to interact with the button to modify badge text, icon, title or its enabled state.
Compose Action
A compose action adds a button to the toolbar of the composer window:
It is controlled by compose_action manifest key in the extension's manifest.json file:
"compose_action": {
    "default_title": "Expand lists",
    "default_icon" : "lists.png",
    "default_popup": "compose_popup.html"
},
If a default_popup is defined, a popup will be opened and the defined html page will be loaded, when the button is clicked. Additionally, you can use the composeAction API in your background script to interact with the button to modify badge text, icon, title or its enabled state.
Message Display Action
A message display action adds a button to the toolbar of the message view window:
It is controlled by the message_display_action manifest key in the extension's manifest.json file:
"message_display_action": {
    "default_title": "Copy Patch",
    "default_icon" : "patch.png",
    "default_popup": "message_popup.html"
    },
If a default_popup is defined, a popup will be opened and the defined html page will be loaded, when the button is clicked. Additionally, you can use the messageDisplayAction API in your background script to interact with the button to modify badge text, icon, title or its enabled state.
CloudFile Provider Configuration
Thunderbird supports cloud providers to upload large attachments to a server, instead of attaching them directly to the email. Extensions can register such cloud providers using the CloudFile API. These providers can be managed in Thunderbird's Composition options:
Menu Items
The menus API allows modifying Thunderbird's menus by adding or overriding menu items. The menu items can be added to different menus based on the provided context type. The following values are currently supported:
Context
Description
Example
tab
Context menu of tab ribbons.
​
​
message_list
Context menu of the message list area of a mail tab. Not limited to a message list entry.
​
​
folder_pane
Context menu of the folder pane of mail tabs. Not limited to a folder entry.
​
​
link
Context menu of links in WebExtension windows, in web tabs or in message display tabs.
Limited to content areas.
​
​
selection
Context menu in WebExtension windows, web tabs or message display tabs, if any text has been selected.
Limited to content areas.
​
​
editable,
password
Context menu of text/password input fields in WebExtension windows, web tabs or message display tabs.
Limited to content areas.
​
​
image,
audio,
video
Context menu of embedded images, audio or video players in WebExtension windows, web tabs or message display tabs.

Limited to content areas.
​
​
page,
frame
Context menu of WebExtension windows, web tabs or message display tabs, if none of the other content contexts apply (link, selection, image, audio, video, editable, password).
If the page is loaded inside a frame, the frame context applies, otherwise the page context. Limited to content areas.
​
​
all
All allowed contexts, excluding tab.
​
``
Supported Manifest Keys
Supported WebExtension APIs
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Browser Action
Compose Action
Message Display Action
CloudFile Provider Configuration
Menu Items