The implemention of nsIPluginInstance::GetValue exits when the key is unknown to the java plugin. There various ways to handle the unknown key in the GetValue. You can return an error or even just leave the return value unmodified. Quitting the program is the most unexpected one. It is such a bad design that makes the browser impossible to extend. All the workarround in browser side force us to write code awaring the implemention of each plugin instead of just the interface. -descripted by Robin.lu