/usr/lib/firefox/distribution/ is in firefox-locale-de 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/de/
/usr/lib/firefox/distribution/searchplugins/locale/de/amazondotcom-de.xml
/usr/lib/firefox/distribution/searchplugins/locale/de/bing.xml
/usr/lib/firefox/distribution/searchplugins/locale/de/duckduckgo.xml
/usr/lib/firefox/distribution/searchplugins/locale/de/eBay-de.xml
/usr/lib/firefox/distribution/searchplugins/locale/de/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/de/leo_ende_de.xml
/usr/lib/firefox/distribution/searchplugins/locale/de/wikipedia-de.xml
/usr/lib/firefox/distribution/searchplugins/locale/de/yahoo-de.xml