/usr/lib/thunderbird/distribution/searchplugins/ is in thunderbird-locale-he 1:24.4.0+build1-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/thunderbird/distribution/searchplugins/locale/
/usr/lib/thunderbird/distribution/searchplugins/locale/he/
/usr/lib/thunderbird/distribution/searchplugins/locale/he/amazondotcom.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/he/aol-web-search.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/he/bing.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/he/eBay.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/he/google.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/he/twitter.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/he/wikipedia.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/he/yahoo.xml