And this (French) forum post has more insights: https://forum.ubuntu- fr.org/viewtopic.php?pid=22359410.
I can reliably reproduce the problem by doing the following (on my system where the locale is fr): sudo apt remove thunderbird-locale-fr find ~/.thunderbird -name langpack...@thunderbird.mozilla.org.xpi -exec rm {} \; # launch thunderbird (now in English), open the Add-ons Manager, search for "Français" and install the first result ("Français Language Pack (Thunderbird)") # close thunderbird, and open it again, and observe the popup with the XML parsing error -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1901829 Title: thunderbird fails to open, xml parse error To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/thunderbird/+bug/1901829/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs