The Unix port of the new Java Plug-In needs knowledge of the fact that the XToolkit is not the default in JDK 5 on Solaris platforms and to specify -Dawt.toolkit=sun.awt.X11.XToolkit. Currently it will attempt to always instantiate an XEmbeddedFrame and fail with the following stack trace:

java.lang.reflect.InvocationTargetException
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:494)
at sun.plugin2.main.client.PluginMain.createEmbeddedFrame(Unknown Source)
at sun.plugin2.main.client.PluginMain.access$100(Unknown Source)
at sun.plugin2.main.client.PluginMain$1.run(Unknown Source)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:461)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)
Caused by: java.lang.ClassCastException: sun.awt.motif.MToolkit
at sun.awt.X11.XEmbeddedFrame.<init>(XEmbeddedFrame.java:31)
... 14 more

Additionally, the new plug-in needs to understand that the XToolkit is not available in 1.4.2 and probably forbid the usage of that platform with the multiple JRE selection functionality. Either that or the XEmbed fixes to the MToolkit that appear in JDK 5 need to be backported to the 1.4.2 train, and the new plug-in modified to use an MEmbeddedFrame instead of an XEmbeddedFrame when the MToolkit is in use.