/usr/ is in thunderbird-locale-da 1:24.4.0+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/da/
/usr/lib/thunderbird/distribution/searchplugins/locale/da/bing.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/da/amazon-co-uk.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/da/eBay.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/da/wikipedia-da.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/da/google.xml
/usr/lib/thunderbird-addons/
/usr/lib/thunderbird-addons/extensions/
/usr/lib/thunderbird-addons/extensions/langpack-da@thunderbird.mozilla.org.xpi
/usr/share/
/usr/share/doc/
/usr/share/doc/thunderbird-locale-da/
/usr/share/doc/thunderbird-locale-da/copyright
/usr/share/doc/thunderbird-locale-da/changelog.Debian.gz