What’s New

1. S/MIME popup shows signature, digest, encryption algorithms and key sizes
2. Default address book for manually added contacts configurable with mail.addr_book.add_item_default_uri
3. Enterprise policy DisableQRExport can disable QR export
4. OAuth add-ons can override built-in settings for selected domains and hostnames
5. Manual account config streamlined with Exchange, Graph, and custom OAuth support
6. Custom OAuth support for IMAP and SMTP servers
7. PKCE and external browser fields added to custom OAuth settings
8. Enterprise policy DisableExperimentalFeatures for disabling experimental features

https://www.thunderbird.net/en-US/thunderbird/155.0/releasenotes