/usr/share/xul-ext/ is in xul-ext-custom-tab-width 1.0.1-2.
This file is owned by root:root, with mode 0o755.
..
/usr/share/xul-ext/custom-tab-width/
/usr/share/xul-ext/custom-tab-width/chrome/
/usr/share/xul-ext/custom-tab-width/chrome.manifest
/usr/share/xul-ext/custom-tab-width/chrome/content/
/usr/share/xul-ext/custom-tab-width/chrome/content/browser.css
/usr/share/xul-ext/custom-tab-width/chrome/content/browser.js
/usr/share/xul-ext/custom-tab-width/chrome/content/browser.xul
/usr/share/xul-ext/custom-tab-width/chrome/content/icon.png
/usr/share/xul-ext/custom-tab-width/chrome/content/options.xul
/usr/share/xul-ext/custom-tab-width/defaults/
/usr/share/xul-ext/custom-tab-width/defaults/preferences/
/usr/share/xul-ext/custom-tab-width/defaults/preferences/000system.js
/usr/share/xul-ext/custom-tab-width/defaults/preferences/defaults.js
/usr/share/xul-ext/custom-tab-width/install.rdf