Instead of

partial interface Navigator {
 DOMstring? userSetting (DOMString key);
 void addUserSettingListener (DOMString key, UserSettingListener callback);
 void removeUserSettingListener (DOMString key, UserSettingListener callback);
};

it should be

partial interface Navigator {
 DOMString? userSetting (DOMString key);
 void addUserSettingListener (DOMString key, UserSettingListener callback);
 void removeUserSettingListener (DOMString key, UserSettingListener callback);
};

The first "s" in the first DOMString is lowercase but should be uppercase.