/usr/share/xul-ext/greasemonkey/content/ is in xul-ext-greasemonkey 3.8-1~deb8u1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/xul-ext/greasemonkey/content/addons4-overlay.js
/usr/share/xul-ext/greasemonkey/content/addons4-overlay.xul
/usr/share/xul-ext/greasemonkey/content/addons4.xul
/usr/share/xul-ext/greasemonkey/content/bindings.xml
/usr/share/xul-ext/greasemonkey/content/browser.js
/usr/share/xul-ext/greasemonkey/content/browser.xul
/usr/share/xul-ext/greasemonkey/content/closewindow.xul
/usr/share/xul-ext/greasemonkey/content/config.js
/usr/share/xul-ext/greasemonkey/content/framescript.js
/usr/share/xul-ext/greasemonkey/content/install.js
/usr/share/xul-ext/greasemonkey/content/install.xul
/usr/share/xul-ext/greasemonkey/content/menucommander.js
/usr/share/xul-ext/greasemonkey/content/newscript.js
/usr/share/xul-ext/greasemonkey/content/newscript.xul
/usr/share/xul-ext/greasemonkey/content/options.js
/usr/share/xul-ext/greasemonkey/content/options.xul
/usr/share/xul-ext/greasemonkey/content/scratchpad-overlay.js
/usr/share/xul-ext/greasemonkey/content/scratchpad-overlay.xul
/usr/share/xul-ext/greasemonkey/content/scriptprefs.js
/usr/share/xul-ext/greasemonkey/content/scriptprefs.xul
/usr/share/xul-ext/greasemonkey/content/third-party/
/usr/share/xul-ext/greasemonkey/content/third-party/addons4.css
/usr/share/xul-ext/greasemonkey/content/third-party/mpl-utils.js