On Firefox and mozilla based browsers JavaScript can make direct calls to Java APIs e.g. java.lang.System.out.println can be used to display a message on the Java Console.
This functionality is not working on FF3 while it works on all of the previous versions of
the mozilla family.
Try running the testcases from the following page with FF3 and older versions of the mozilla and FF family.
http://sqeweb/deployment2/jitu/deployment_JDK7_int_ws/deployment/src/plugin/manual/html/DirectTest.html

On FF3 following is the behavior using old and new Plug-in
Old Plug-in
-----------
Boolen tests:
None of the testcases works

Char Tests:
None of the testcases works

Enumeration test:
Half of them work

Numeric tests : All Passed

Null tests : ALL Passed

Other Java APIs(java.awt, java.lang and javax.swing) : All PASSED

New PLug-in:
-----------
Boolen tests:
Some of the testcases works

Char Tests:
NOne of them worked

Enumeration test: All PASSED

Numeric tests : Some of the tests FAILED

Null tests : ALL Passed

Java APIs(java.awt, java.lang and javax.swing) :
Some of them FAILED
Javascript errors of following type is getting thrown while calling the java APIs
Error: uncaught exception: Error calling method on NPObject! [plugin exception: java.lang.IllegalArgumentException: More than one method matching name java.util.Date and arguments [java.lang.Integer]].