/usr/lib/firefox/ is in firefox-locale-si 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-si@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/si/
/usr/lib/firefox/distribution/searchplugins/locale/si/amazondotcom.xml
/usr/lib/firefox/distribution/searchplugins/locale/si/answers.xml
/usr/lib/firefox/distribution/searchplugins/locale/si/creativecommons.xml
/usr/lib/firefox/distribution/searchplugins/locale/si/eBay.xml
/usr/lib/firefox/distribution/searchplugins/locale/si/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/si/wikipedia-si.xml
/usr/lib/firefox/distribution/searchplugins/locale/si/yahoo.xml