/usr/ is in lightning-l10n-ga-ie 1:52.9.1-1~deb9u1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/
/usr/lib/lightning/
/usr/lib/lightning/extensions/
/usr/lib/thunderbird/
/usr/lib/thunderbird/extensions/
/usr/share/
/usr/share/doc/
/usr/share/doc/lightning-l10n-ga-ie/
/usr/share/doc/lightning-l10n-ga-ie/changelog.Debian.gz
/usr/share/doc/lightning-l10n-ga-ie/copyright
/usr/share/lightning/
/usr/share/lightning/extensions/
/usr/share/lightning/extensions/langpack-ga-ie@lightning.debian.org/
/usr/share/lightning/extensions/langpack-ga-ie@lightning.debian.org/chrome/
/usr/share/lightning/extensions/langpack-ga-ie@lightning.debian.org/chrome/ga-IE.jar
/usr/share/lightning/extensions/langpack-ga-ie@lightning.debian.org/chrome.manifest
/usr/share/lightning/extensions/langpack-ga-ie@lightning.debian.org/install.rdf
/usr/share/lightning/extensions/langpack-ga-ie@lightning.debian.org/uninstall/
/usr/share/lightning/extensions/langpack-ga-ie@lightning.debian.org/uninstall/Uninstall
/usr/share/lintian/
/usr/share/lintian/overrides/
/usr/share/lintian/overrides/lightning-l10n-ga-ie
/usr/lib/lightning/extensions/langpack-ga-ie@lightning.debian.org
/usr/lib/thunderbird/extensions/langpack-ga-ie@lightning.debian.org