/usr/lib/ is in thunderbird-locale-sv 1:38.6.0+build1-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/thunderbird/
/usr/lib/thunderbird/distribution/
/usr/lib/thunderbird/distribution/searchplugins/
/usr/lib/thunderbird/distribution/searchplugins/locale/
/usr/lib/thunderbird/distribution/searchplugins/locale/sv-SE/
/usr/lib/thunderbird/distribution/searchplugins/locale/sv-SE/yahoo.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/sv-SE/tyda-sv-SE.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/sv-SE/wikipedia-sv-SE.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/sv-SE/prisjakt-sv-SE.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/sv-SE/bing.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/sv-SE/google.xml
/usr/lib/thunderbird-addons/
/usr/lib/thunderbird-addons/extensions/
/usr/lib/thunderbird-addons/extensions/langpack-sv-SE@thunderbird.mozilla.org.xpi