/usr/lib/ is in thunderbird-locale-pt 1:24.4.0+build1-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/thunderbird/
/usr/lib/thunderbird/distribution/
/usr/lib/thunderbird/distribution/searchplugins/
/usr/lib/thunderbird/distribution/searchplugins/locale/
/usr/lib/thunderbird/distribution/searchplugins/locale/pt-PT/
/usr/lib/thunderbird/distribution/searchplugins/locale/pt-PT/wikipedia-ptpt.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/pt-PT/amazon-en-GB.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/pt-PT/priberam.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/pt-PT/sapo.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/pt-PT/google.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/pt-BR/
/usr/lib/thunderbird/distribution/searchplugins/locale/pt-BR/bing.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/pt-BR/amazondotcom.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/pt-BR/eBay.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/pt-BR/yahoo.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/pt-BR/aol-web-search.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/pt-BR/twitter.xml
/usr/lib/thunderbird/distribution/searchplugins/locale/pt-BR/wikipedia.xml
/usr/lib/thunderbird-addons/
/usr/lib/thunderbird-addons/extensions/
/usr/lib/thunderbird-addons/extensions/langpack-pt-PT@thunderbird.mozilla.org.xpi
/usr/lib/thunderbird-addons/extensions/langpack-pt-BR@thunderbird.mozilla.org.xpi