/usr/lib/firefox/distribution/ is in firefox-locale-es 28.0+build2-0ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/firefox/distribution/searchplugins/
/usr/lib/firefox/distribution/searchplugins/locale/
/usr/lib/firefox/distribution/searchplugins/locale/es-AR/
/usr/lib/firefox/distribution/searchplugins/locale/es-AR/amazondotcom.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-AR/creativecommons.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-AR/drae.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-AR/duckduckgo.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-AR/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-AR/mercadolibre-ar.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-AR/wikipedia-es.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-AR/yahoo-ar.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-CL/
/usr/lib/firefox/distribution/searchplugins/locale/es-CL/bing.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-CL/drae.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-CL/duckduckgo.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-CL/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-CL/mercadolibre-cl.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-CL/wikipedia-es.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-CL/yahoo-cl.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-ES/
/usr/lib/firefox/distribution/searchplugins/locale/es-ES/bing.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-ES/drae.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-ES/duckduckgo.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-ES/eBay-es.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-ES/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-ES/twitter.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-ES/wikipedia-es.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-ES/yahoo-es.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-MX/
/usr/lib/firefox/distribution/searchplugins/locale/es-MX/bing.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-MX/duckduckgo.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-MX/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-MX/mercadolibre-mx.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-MX/wikipedia-es.xml
/usr/lib/firefox/distribution/searchplugins/locale/es-MX/yahoo-mx.xml