The glib-gio error is normal. If you could, it would be an idea to run your applications with the help of the menus, and not run Firefox as root : it's a user application and running it as root, even for a test, is not the right thing to do. This type of method almost always, or often if not always changes ownership of files or directories in the home of the user, then things work much less well.
Synaptic can be run from the menus, then the policykit system sends the prompt for root in a window. If you want to use the console, you could use text mode commands.