/usr/lib/thunderbird/distribution/ is in thunderbird-locale-ta 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/ta-LK/
/usr/lib/thunderbird/distribution/searchplugins/locale/ta-LK/amazondotcom.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/ta-LK/aol-web-search.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/ta-LK/bing.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/ta-LK/eBay.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/ta-LK/twitter.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/ta-LK/wikipedia.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/ta-LK/yahoo.xml