Thunderbird 78.9.0 is a bug fix and security release

Martin Brinkmann
Mar 25, 2021
Email, Thunderbird

A new stable version of the Thunderbird email client has been released on March 23, 2021. Thunderbird 78.9.0 is a bug fix and security update for all stable versions of the email program (Mac, Windows and Linux). The update was released on the same day that the new Mozilla Firefox stable version was released.

The new version of Thunderbird is already available as a direct download from the official Thunderbird website, and as an in-browser update. Select Help > About Thunderbird to display the installed version and run a manual check for updates.

Thunderbird 78.9.9 fixes five security issues with severity ratings of high and moderate. High is the second highest rating after critical.

  • CVE-2021-23981: Texture upload into an unbound backing buffer resulted in an out-of-bound read (HIGH)
  • MOZ-2021-0002: Angle graphics library out of date (HIGH)
  • CVE-2021-23987: Memory safety bugs fixed in Thunderbird 78.9 (HIGH)
  • CVE-2021-23982: Internal network hosts could have been probed by a malicious webpage (MODERATE)
  • CVE-2021-23984: Malicious extensions could have spoofed popup information  (MODERATE)

The remaining changes in the new Thunderbird version address various issues of previous client versions. The notification system got another fix in this release as it happened that old unread messages were displayed by it repeatedly during new mail events. Thunderbird users who use the integrated calendar may have noticed that it was not possible to remove recurring tasks; this has been fixed in Thunderbird 78.9.0 as well.

The address book received three fixes:

  • The synchronization of read-only Google address books via CardDAV failed in previous versions; this is fixed.
  • The importing of VCards with non-ASCII characters would fail; this is also fixed.
  • The synchronization from Google address books could result in some values not being parsed; fixed as well.

The new update addresses an encoding issue for messages with quoted-printable and format=flowed. The issue is fixed, but existing messages may display some words that are not separated by a space as a consequence.

Messages that contained an anchor tag with an invalid data URI failed automatically when the send button was activated.

The developers made several accessibility improvements: some fields in the preferences were not readable in dark theme mode, and the input focus was not moved to the new tab when switching tab. Both of these are addressed in Thunderbird 78.9.0.

The release notes list a single known issues. The fix for new mail notifications not showing if unread messages from previous notifications were still there, has been removed. The team is working on a resolution.

Thunderbird 78.9.0 is a bug fix and security release
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Thunderbird 78.9.0 is a bug fix and security release
A new stable version of the Thunderbird email client has been released on March 23, 2021. Thunderbird 78.9.0 is a bug fix and security update.
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  1. JMGG said on January 19, 2012 at 8:25 am

    You said that Outlook isn’t your main email client, so which is your main one?

    1. BalaC said on January 19, 2012 at 9:42 am

      I think its thunderbird

    2. Martin Brinkmann said on January 19, 2012 at 10:15 am

      It is Mozilla Thunderbird.

  2. Salaam said on September 24, 2012 at 9:52 pm

    Awesome! This actually solved my problem… what a stupid bug.

  3. Claud said on December 19, 2012 at 2:08 am

    If this is the same bug that I’ve encountered, there may be another fix: (1) hover over open Outlook item in Taskbar, cursor up to hover over Outlook window item, and right-click; (2) this should give you Restore / Move / Size / Minimize / Maximize — choose Move or Size; (3) use your cursor keys, going arbitrarily N/S/E/W, to try to move or size the Outlook window back into view. Basically, the app behaves as though it were open in a 0x0 window, or at a location that’s offscreen, and this will frequently work to resize and/or move the window. Don’t forget to close while resized/moved, so that Outlook remembers the size/position for next time.

    1. Lynda said on February 12, 2013 at 3:37 pm

      THANK YOU Claude!!! I could get the main window to launch but could not get any other message window to show on the desktop. You are my hero!!!!

    2. Chad said on November 20, 2018 at 4:24 pm

      Solved my issue! 6 years later and this is still problem…

    3. Ivan X said on January 21, 2021 at 4:50 pm

      Fantastic. Thank you. Size did the trick.

  4. Andrew said on October 26, 2013 at 7:06 am

    This solved my Outlook problem, too. Thank you. :)

  5. Charles said on December 7, 2013 at 7:23 pm

    Thank you so much, this started happening to me today and was causing big problems. You are a life saver, I hope I can help you in some way some day.

  6. garth said on November 7, 2014 at 7:13 pm

    You are a god – thank you!

  7. Faisal said on February 9, 2015 at 10:09 am

    thanks a lot…. work like charm.. :-)

  8. Simon said on March 24, 2015 at 11:36 pm

    Yah…thanks Claude. I’ve been having the same problem and tried all the suggestions…your solution was the answer. It had resized itself to a 0/0 box. Cheers

  9. Olu said on April 14, 2015 at 1:35 pm

    Excellent post. This had me baffled even trying to accurately describe the problem. This fixed it for me.
    Thank you

  10. Coenig said on July 23, 2015 at 7:36 am

    Thanks a lot for the article. Don’t know why it happenend, don’t know how it got fixed, but it was really annoying and now it works :-)

  11. Fali said on January 20, 2016 at 4:19 pm

    Thanks a lot. I was facing this issue from past 3 week. I tried everything but no resolution. The issue was happening intermittently and mainly when I was changing the display of screen ( as i use 2 monitors). The only option i had was to do system restore. But thanks to you.

    1. MIki said on January 10, 2019 at 11:54 am

      I’ve been tried to sole this problem for 12hours. Your comment about changing the display of screen helped me a lot!! Thanks!!

  12. Christina said on January 20, 2016 at 6:14 pm

    Thank you…don’t know why this happened but your instructions helped me fix it. Running Windows 10 and office pro 2007

  13. Oz said on July 22, 2016 at 3:20 pm

    Great tip! Thanks!

  14. Tracy said on September 1, 2016 at 4:48 pm

    Worked for me, too – thank you!!!

  15. shawn said on September 9, 2016 at 10:25 am

    It’s Worked for me, too
    thank you very much!

  16. Jari said on October 31, 2016 at 11:53 am

    I had a similar issue with Outlook 2013 on Windows 10 and this helped me to fix it. Thank you very much!

  17. Michel H said on November 30, 2016 at 11:08 pm

    Thank you so much. Solved!
    Considering you published this in 2012, incredible not been debugged by Microsoft.
    Thank you again. M

  18. Ziad Bitar said on January 9, 2017 at 2:00 am

    This problem was faced by only one user logging to TS 2008 r2 using outlook 2010.The issue was resolved.


  19. Anonymous said on February 15, 2017 at 5:24 pm

    Great tip. Thank you!!!! If it helps, I had to use the Control Key and the arrow keys at the same time to bring my window back into view. Worked like a charm.

  20. Rochelle said on March 6, 2017 at 11:59 am

    Thank you, this worked !!!!

  21. anom1234 said on May 20, 2018 at 11:20 pm

    Man, you are a fucking god. Thanks a lot, what an annoying bug!!

  22. JC said on October 12, 2020 at 2:14 pm

    Awesome, this post solved the issue. Many thanks!

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