/usr/lib/ is in thunderbird-locale-ca 1:24.4.0+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/ca/
/usr/lib/thunderbird/distribution/searchplugins/locale/ca/diec2.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/ca/llibres.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/ca/bing.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/ca/wikipedia-ca.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/ca/huubs.xml
/usr/lib/thunderbird-addons/
/usr/lib/thunderbird-addons/extensions/
/usr/lib/thunderbird-addons/extensions/langpack-ca@thunderbird.mozilla.org.xpi