Software Update: Mozilla Thunderbird 78.4.0

The Mozilla Foundation has released version 78.4 of Thunderbird. Thunderbird is an open source client for email and newsgroups, with features such as support for several 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:

What’s New:

  • MailExtensions: browser.tabs.sendMessage API added
  • MailExtensions: messageDisplayScripts API added


  • Yahoo and AOL mail users using password authentication will be migrated to OAuth2
  • MailExtensions: messageDisplay APIs extended to support multiple selected messages
  • MailExtensions: compose.begin functions now support creating a message with attachments


  • Thunderbird could freeze when updating global search index
  • Multiple issues with handling of self-signed SSL certificates addressed
  • Recipient address fields in compose window could expand to fill all available space
  • Inserting emoji characters in message compose window caused unexpected behavior
  • Button to restore default folder icon color was not keyboard accessible
  • Various keyboard navigation fixes
  • Various color-related theme fixes
  • MailExtensions: Updating attachments with onBeforeSend.addListener() did not work
  • Various security fixes

Version number 78.4.0
Release status Final
Operating systems Windows 7, Linux, macOS, Windows 8, Windows 10
Website Mozilla Foundation
License type GPL