/usr/lib/firefox/distribution/searchplugins/ is in firefox-locale-be 28.0+build2-0ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/firefox/distribution/searchplugins/locale/
/usr/lib/firefox/distribution/searchplugins/locale/be/
/usr/lib/firefox/distribution/searchplugins/locale/be/be-x-old.wikipedia.org.xml
/usr/lib/firefox/distribution/searchplugins/locale/be/be.wikipedia.org.xml
/usr/lib/firefox/distribution/searchplugins/locale/be/duckduckgo.xml
/usr/lib/firefox/distribution/searchplugins/locale/be/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/be/ru.wikipedia.org-be.xml
/usr/lib/firefox/distribution/searchplugins/locale/be/tut.by.xml
/usr/lib/firefox/distribution/searchplugins/locale/be/yahoo.xml
/usr/lib/firefox/distribution/searchplugins/locale/be/yandex.ru-be.xml