/usr/lib/ is in firefox-locale-csb 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/csb/
/usr/lib/firefox/distribution/searchplugins/locale/csb/allegro-pl.xml
/usr/lib/firefox/distribution/searchplugins/locale/csb/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/csb/pwn-pl.xml
/usr/lib/firefox/distribution/searchplugins/locale/csb/fbc-pl.xml
/usr/lib/firefox/distribution/searchplugins/locale/csb/duckduckgo.xml
/usr/lib/firefox/distribution/searchplugins/locale/csb/wp-pl.xml
/usr/lib/firefox/distribution/searchplugins/locale/csb/merlin-pl.xml
/usr/lib/firefox/distribution/searchplugins/locale/csb/wikipedia-csb.xml
/usr/lib/firefox-addons/
/usr/lib/firefox-addons/extensions/
/usr/lib/firefox-addons/extensions/langpack-csb@firefox.mozilla.org.xpi