writes the current user prefs dictionary to disk

def _write_user_prefs(self, user_prefs):
        """
        writes the current user prefs dictionary to disk
        """
        with open(self.userPrefs, "w") as f:
            for key, value in user_prefs.items():
                f.write('user_pref("%s", %s);\n' % (key, json.dumps(value)))