/usr/lib/firefox/distribution/ is in firefox-locale-eo 11.0+build1-0ubuntu4.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/firefox/distribution/searchplugins/
/usr/lib/firefox/distribution/searchplugins/locale/
/usr/lib/firefox/distribution/searchplugins/locale/eo/
/usr/lib/firefox/distribution/searchplugins/locale/eo/amazondotcom.xml
/usr/lib/firefox/distribution/searchplugins/locale/eo/bing.xml
/usr/lib/firefox/distribution/searchplugins/locale/eo/creativecommons.xml
/usr/lib/firefox/distribution/searchplugins/locale/eo/eBay.xml
/usr/lib/firefox/distribution/searchplugins/locale/eo/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/eo/reta-vortaro.xml
/usr/lib/firefox/distribution/searchplugins/locale/eo/wikipedia-eo.xml
/usr/lib/firefox/distribution/searchplugins/locale/eo/yahoo.xml