/usr/share/xul-ext/firegestures/chrome/content/ is in xul-ext-firegestures 1.10.9-1~deb8u1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/xul-ext/firegestures/chrome/content/firegestures/
/usr/share/xul-ext/firegestures/chrome/content/firegestures/bindings.xml
/usr/share/xul-ext/firegestures/chrome/content/firegestures/browser.js
/usr/share/xul-ext/firegestures/chrome/content/firegestures/browser.rdf
/usr/share/xul-ext/firegestures/chrome/content/firegestures/browser.xul
/usr/share/xul-ext/firegestures/chrome/content/firegestures/edit.js
/usr/share/xul-ext/firegestures/chrome/content/firegestures/edit.xul
/usr/share/xul-ext/firegestures/chrome/content/firegestures/prefs-generic.xul
/usr/share/xul-ext/firegestures/chrome/content/firegestures/prefs.js
/usr/share/xul-ext/firegestures/chrome/content/firegestures/prefs.xul
/usr/share/xul-ext/firegestures/chrome/content/firegestures/remote.js
/usr/share/xul-ext/firegestures/chrome/content/firegestures/selectDialog.xul
/usr/share/xul-ext/firegestures/chrome/content/firegestures/viewSource.js
/usr/share/xul-ext/firegestures/chrome/content/firegestures/viewSource.rdf
/usr/share/xul-ext/firegestures/chrome/content/firegestures/viewSource.xul