/usr/lib/thunderbird/distribution/ is in thunderbird-locale-hy 1:38.6.0+build1-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/thunderbird/distribution/searchplugins/
/usr/lib/thunderbird/distribution/searchplugins/locale/
/usr/lib/thunderbird/distribution/searchplugins/locale/hy-AM/
/usr/lib/thunderbird/distribution/searchplugins/locale/hy-AM/amazondotcom.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/hy-AM/aol-web-search.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/hy-AM/bing.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/hy-AM/eBay.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/hy-AM/twitter.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/hy-AM/wikipedia.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/hy-AM/yahoo.xml