Changes in Thunderbird 98

accounts API

added manifest property reuse_uploads, to allow providers to disable automatic link reuse of already known cloud files: If a previously uploaded cloud file attachment is reused at a later time in a different message, Thunderbird may use the already known url and templateInfo values without triggering the registered onFileUpload listener again. Setting this option to false will always trigger the registered listener, providing the already known values through the relatedFileInfo parameter of the onFileUpload event, to let the provider decide how to handle these cases.
added the relatedFileInfo parameter of the onFileUpload event: Information about an already uploaded cloud file, which is related to a new upload. For example if the content of a cloud attachment is updated, if a repeatedly used cloud attachment is renamed (and therefore should be re-uploaded to not invalidate existing links) or if the provider has its manifest property reuse_uploads set to false.

deprecated the getFile() function of the ComposeAttachment (example of a backward-compatible drop-in wrapper function)
added getAttachmentFile(id) function to get the content of a ComposeAttachment as a DOM File object
added support to use a ComposeAttachment as the attachment in addAttachment(tabId, attachment) and in ComposeDetails
modified the rules for body, plainTextBody and isPlainText properties of ComposeDetails in a backward compatible way - specifying both body types no longer causes an exception and it is now even suggested to always specify both and either let the API pick the users default compose mode, or use the isPlainText property as selector

Bugzilla list of fixed WebExtension API defects in Thunderbird 98.