/usr/ is in thunderbird-locale-pl 1:38.6.0+build1-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/
/usr/lib/thunderbird/
/usr/lib/thunderbird/distribution/
/usr/lib/thunderbird/distribution/searchplugins/
/usr/lib/thunderbird/distribution/searchplugins/locale/
/usr/lib/thunderbird/distribution/searchplugins/locale/pl/
/usr/lib/thunderbird/distribution/searchplugins/locale/pl/merlin-pl.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/pl/pwn-pl.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/pl/wolnelektury-pl.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/pl/allegro-pl.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/pl/google.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/pl/wikipedia-pl.xml
/usr/lib/thunderbird-addons/
/usr/lib/thunderbird-addons/extensions/
/usr/lib/thunderbird-addons/extensions/langpack-pl@thunderbird.mozilla.org.xpi
/usr/share/
/usr/share/doc/
/usr/share/doc/thunderbird-locale-pl/
/usr/share/doc/thunderbird-locale-pl/copyright
/usr/share/doc/thunderbird-locale-pl/changelog.Debian.gz