/usr/lib/thunderbird/distribution/ is in thunderbird-locale-zh-hant 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/zh-TW/
/usr/lib/thunderbird/distribution/searchplugins/locale/zh-TW/chunghwapost-zh-TW.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/zh-TW/findbook-zh-TW.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/zh-TW/google-maps-zh-TW.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/zh-TW/google.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/zh-TW/ipeen-zh-TW.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/zh-TW/wikipedia-zh-TW.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/zh-TW/yahoo-bid-zh-TW.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/zh-TW/yahoo-zh-TW.xml