/usr/lib/ is in thunderbird-locale-ga 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/ga-IE/
/usr/lib/thunderbird/distribution/searchplugins/locale/ga-IE/eBay-en-GB.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/ga-IE/focal.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/ga-IE/twitter.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/ga-IE/yahoo-en-GB.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/ga-IE/wikipedia-ga-IE.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/ga-IE/amazon-en-GB.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/ga-IE/google.xml
/usr/lib/thunderbird-addons/
/usr/lib/thunderbird-addons/extensions/
/usr/lib/thunderbird-addons/extensions/langpack-ga-IE@thunderbird.mozilla.org.xpi