Changes in Thunderbird 78.5.0

compose

• ComposeAttachment objects now have a size property with the size of the attachment in bytes.

menus

• A compose_attachment context can now be used. This context applies when the user opens a context menu on selected attachments in a compose window. The selected attachments can be accessed from the attachments property in the onClicked listener.

tabs

• At start-up, tabs.create will now wait for a window to open before attempting to open a tab.