The getProps() implementation in ClientConfig and EmptyConfig just returned :
new Properties(this);
it should be returning :
(Properties) this.clone();

The above Constructor only creates a Properties object with the defaults of the given Properties object, not with all properties of the given properties object.

Also it is noticed that
src/plugin/share/classes/sun/plugin/AppletViewer.java, and
src/plugin/share/classes/sun/plugin2/applet/Applet2Environment.java

call:
    Properties configProps = Config.get().getProps();
and then never use the returned configProps object, since this is fairly expensive,
we will remove these two lines also.

Then the only remaining place this is used is when user enters "S" to the console, and in unit test programs.