/usr/lib/firefox/ is in firefox-locale-sk 11.0+build1-0ubuntu4.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/firefox-addons/extensions/
/usr/lib/firefox-addons/extensions/langpack-sk@firefox.mozilla.org.xpi
/usr/lib/firefox/distribution/
/usr/lib/firefox/distribution/searchplugins/
/usr/lib/firefox/distribution/searchplugins/locale/
/usr/lib/firefox/distribution/searchplugins/locale/sk/
/usr/lib/firefox/distribution/searchplugins/locale/sk/atlas-sk.xml
/usr/lib/firefox/distribution/searchplugins/locale/sk/azet-sk.xml
/usr/lib/firefox/distribution/searchplugins/locale/sk/dunaj-sk.xml
/usr/lib/firefox/distribution/searchplugins/locale/sk/eBay.xml
/usr/lib/firefox/distribution/searchplugins/locale/sk/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/sk/slovnik-sk.xml
/usr/lib/firefox/distribution/searchplugins/locale/sk/wikipedia-sk.xml
/usr/lib/firefox/distribution/searchplugins/locale/sk/zoznam-sk.xml