When starting Thunderbird in Ubuntu 20.10 an error message is displayed

XML Parsing Error: undefined entity
Location: chrome://messenger/content/messenger.xhtml
Line Number 905, Column 3:
  <key id="openLightningKey"

and nothing more happens. However Thunderbird can be started in "safe mode" with the command line command

thunderbird -safe-mode

I have a number of language packs installed, German, English (CA), English (GB), French and Swedish.

How can I make Thunderbird start OK from the apllications menu?

  • 1
    Did you install any dictionaries/language packs by any chance?
    – Kay
    Oct 28, 2020 at 17:07

4 Answers 4


I was experiencing the same problem just earlier after installing an official language pack by Mozilla. After closing and restarting Thunderbird, I was shown a popup with the exact same message you posted, and couldn't get Thunderbird running again.

Based on messages in this (German language) forum thread: https://www.thunderbird-mail.de/forum/thread/85658-thunderbird-startet-nicht-bzw-gibt-fehlermeldung-nur-im-safemode-m%C3%B6glich/?postID=468615, others are having the same problem, also after having recently installed or updated language packs.

I managed to solve the problem on my end by moving the offending file (langpack-en-GB@thunderbird.mozilla.org.xpi, in my case) out of Thunderbird's extensions directory. On my system, all my Thunderbird settings, including the exensions directory, reside at /home/MYUSER/.thunderbird/RANDOMSTRING.default.

  • This helped, thank you. In my case it was langpack-nl@.... After removing this file, I would expect the interface to be in English, but it still presents Dutch.
    – Jos
    Oct 29, 2020 at 16:46
  • Nice catch, fixed it on my side using mv langpack-fr@thunderbird.mozilla.org.xpi ../ in the following directory: /home/user/.thunderbird/8rz2sdbv.default/extensions
    – egdavid
    Nov 2, 2020 at 14:21

I managed to work around this issue on Ubuntu 20.10 by starting with thunderbird --safe-mode and removing all language packs (menu "Add-ons" -> "Languages"). Note that on my system I wasn't able to remove all of them since some of them were installed from Debian packages. Turns out the latter weren't causing any problems, though, and I was able to start Thunderbird without safe-mode.

In case you want to remove the language packs installed from Debian packages as well you can do so by running (adjust according to the languages installed on your machine):

$ apt purge thunderbird-locale-de thunderbird-locale-en

After doing so the list of language packs should be empty and you should be able to start Thunderbird normally.

  • This worked for me! (Ubuntu 20.10) Especially the first part: open thunderbird in safe mode and disable the language packages. Restart without safemode Nov 12, 2020 at 20:55

The accepted answer did not helped me but this did:

  1. start thunderbird in the command line/shell/terminal with thunderbird --safe-mode
  2. choose "disable all add-ons" and
  3. click the button "Make changes and restart". Then it can be started as usual like using the the normal thunderbird start icons or thunderbird in the command line/shell/terminal.

Maybe this is a more elegant solution for users that do not want or can move files in the configuration directories.


In particular in fedora 31 with TB 78.3.1 (64-bit), I went to /home/MYUSER/.thunderbird/RANDOMSTRING.default/extensions and did following (which eliminated the problem).

% mkdir suspect
% mv langpack-en* suspect
  • Your answer seems to be a duplicate of my original solution.
    – Kay
    Oct 31, 2020 at 9:37

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