/usr/lib/firefox/distribution/searchplugins/ is in firefox-locale-nb 28.0+build2-0ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/firefox/distribution/searchplugins/locale/
/usr/lib/firefox/distribution/searchplugins/locale/nb-NO/
/usr/lib/firefox/distribution/searchplugins/locale/nb-NO/amazon-en-GB.xml
/usr/lib/firefox/distribution/searchplugins/locale/nb-NO/bing.xml
/usr/lib/firefox/distribution/searchplugins/locale/nb-NO/bok-NO.xml
/usr/lib/firefox/distribution/searchplugins/locale/nb-NO/duckduckgo.xml
/usr/lib/firefox/distribution/searchplugins/locale/nb-NO/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/nb-NO/gulesider-NO.xml
/usr/lib/firefox/distribution/searchplugins/locale/nb-NO/qxl-NO.xml
/usr/lib/firefox/distribution/searchplugins/locale/nb-NO/wikipedia-NO.xml
/usr/lib/firefox/distribution/searchplugins/locale/nb-NO/yahoo-NO.xml