/usr/lib/firefox/ is in firefox-locale-bn 28.0+build2-0ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/firefox-addons/extensions/
/usr/lib/firefox-addons/extensions/langpack-bn-BD@firefox.mozilla.org.xpi
/usr/lib/firefox-addons/extensions/langpack-bn-IN@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/bn-BD/
/usr/lib/firefox/distribution/searchplugins/locale/bn-BD/bing.xml
/usr/lib/firefox/distribution/searchplugins/locale/bn-BD/duckduckgo.xml
/usr/lib/firefox/distribution/searchplugins/locale/bn-BD/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/bn-BD/wikipedia-bn.xml
/usr/lib/firefox/distribution/searchplugins/locale/bn-BD/yahoo.xml
/usr/lib/firefox/distribution/searchplugins/locale/bn-IN/
/usr/lib/firefox/distribution/searchplugins/locale/bn-IN/amazondotcom.xml
/usr/lib/firefox/distribution/searchplugins/locale/bn-IN/bing.xml
/usr/lib/firefox/distribution/searchplugins/locale/bn-IN/duckduckgo.xml
/usr/lib/firefox/distribution/searchplugins/locale/bn-IN/eBay-in.xml
/usr/lib/firefox/distribution/searchplugins/locale/bn-IN/google.xml
/usr/lib/firefox/distribution/searchplugins/locale/bn-IN/rediff.xml
/usr/lib/firefox/distribution/searchplugins/locale/bn-IN/technorati.xml
/usr/lib/firefox/distribution/searchplugins/locale/bn-IN/wikipedia-bn.xml
/usr/lib/firefox/distribution/searchplugins/locale/bn-IN/yahoo-in.xml