Changes in Thunderbird 96
templateInfoas a supported return value property of the onFileUpload event, to specify a CloudFileTemplateInfo with additional information for the cloud file entry added to the users message
erroras a supported return value property of the onFileUpload event, to show an error message to the user, in case upload failed
added onFileRename event to properly handle cloud file rename operations (the file on the server should be renamed as well, if the cloud file attachment in the email is renamed by the user)
attachmentas a supported property of the query(queryInfo) function, to be able to query for messages with or without attachments
Bugzilla list of fixed WebExtension API defects in Thunderbird 96.