Software Update: Mozilla Thunderbird 78.3.1

The Mozilla Foundation has released version 78.3 of Thunderbird and 78.3.1 has also been released due to frequent crashes. Thunderbird is an open source client for e-mail and newsgroups, with features such as support for various mail and news accounts, a spam filter, spell checker and a customizable appearance. In version 78 we find, among other things, a dark mode and other parts of the interface, such as the icons and the screen for composing an email, have been taken care of. Furthermore, the Lightning calendar add-on is now a standard part of the program, there is a new wizard for the first use and only MailExtensions add-ons are supported. The changelog for this release looks like this:


  • OpenPGP: Improved decryption performance with large messages
  • OpenPGP: Do not show external key UI when disabled by preference
  • Account setup wizard will now open a popup when connecting to a server with a self-signed SSL/TLS certificate
  • Installation of “legacy” MailExtensions now disabled
  • Reply-To header moved in compose window; now appears under From header
  • Calendar: Sidebar UI improvements


  • Selecting “Cancel” on the Master Password prompt at startup incorrectly reported corrupted OpenPGP data
  • OpenPGP: Creating a new key pair did not automatically select it for use
  • Dragging & Dropping recipient pills resulted in lost pills when an error was present
  • Spellcheck suggestions were unreadable in dark theme
  • Calendar: Multiple password prompts opened
  • Linux Distributions: UI was not rendered completely when built without updater
  • MailExtensions: browser.folders.delete failed on IMAP folders
  • Various security fixes

Version number 78.3.1
Release status Final
Operating systems Windows 7, Linux, macOS, Windows 8, Windows 10
Website Mozilla Foundation
License type GPL