Changes in Thunderbird 78
compose
Attachments in the compose window can now be accessed with the compose API. These functions have been added:
These events have been added:
See the documentation on those functions and events for more information.
A new event, onIdentityChanged was added.
identity
The browser.identity namespace for OAuth handling was enabled.
Bugzilla list of fixed WebExtension API defects in Thunderbird 78.