It is recommended to switch from Cookies to interfaces i.e. use Openable instead of OpenCookie. Unfortunately this is not possible yet.

For example when you try to use Openable with org.openide.actions.OpenAction the action will never be enabled. OpenAction defines OpenCookie as the class to lookup for enabling the action. This is also true with many others like  EditAction,
PrintAction, etc.

You can compare OpenAction to SaveAction where Savable is used instead of the old SaveCookie.

Actually the fix is very easy: OpenCookie already implementing Openable, one only needs to return Openable class in method OpenAction.cookieClasses() (at least I suppose it should work like this) instead of OpenCookie.

This would look like:

public class OpenAction extends CookieAction {
    protected Class[] cookieClasses() {
        return new Class[] { Openable.class };
    }
...
}