/usr/lib/ is in firefox-locale-pl 28.0+build2-0ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/firefox/
/usr/lib/firefox/distribution/
/usr/lib/firefox/distribution/searchplugins/
/usr/lib/firefox/distribution/searchplugins/locale/
/usr/lib/firefox/distribution/searchplugins/locale/pl/
/usr/lib/firefox/distribution/searchplugins/locale/pl/allegro-pl.xml
/usr/lib/firefox/distribution/searchplugins/locale/pl/wolnelektury-pl.xml
/usr/lib/firefox/distribution/searchplugins/locale/pl/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/pl/pwn-pl.xml
/usr/lib/firefox/distribution/searchplugins/locale/pl/duckduckgo.xml
/usr/lib/firefox/distribution/searchplugins/locale/pl/wikipedia-pl.xml
/usr/lib/firefox/distribution/searchplugins/locale/pl/wp-pl.xml
/usr/lib/firefox/distribution/searchplugins/locale/pl/merlin-pl.xml
/usr/lib/firefox-addons/
/usr/lib/firefox-addons/extensions/
/usr/lib/firefox-addons/extensions/langpack-pl@firefox.mozilla.org.xpi