How does http://extensions.gnome.org work ? The page displays all the extensions on my computer, and you can install them online with one click. How can this site access the operating system and make changes to my shell?
It interacts with a custom browser plugin called GNOME Shell Integration. See https://extensions.gnome.org/static/js/dbus.js for guts.
Please note that it probably wonβt work outside the GNOME site for obvious security reasons.