The Mozilla "nsIModule" interface is part of what makes an XPCOM component an XPCOM component. The current Java Plug-In does not implement this interface, instead relying on deprecated code that will soon be removed from the Mozilla code base. If this obsolete code in Mozilla is removed and Java Plug-In does not implement nsIModule, the Java Plug-In will not be loaded into the browser, therefore, Java no worky.

By implementing nsIModule, Java Plug-In will be a better-behaved XPCOM component.