STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. open the following url with java console open:
http://sqeweb/jsn/users/fred/deployment_ws/fred/deployment_6_UR_int_ws/deployment/src/plugin/FunctionalTest/FunctionalTest/html/OwnerNodeTest.html

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The following strings are printed:
@@@@ element type is right
@@@@ ownerNode is equal to the node returned by getElementById
@@@@ test pass
ACTUAL -
on firefox, the following exception is raised:
sun.plugin.dom.exception.PluginNotSupportedException: Node.isEqualNode() is not supported.
at sun.plugin.dom.core.Node.isEqualNode(Unknown Source)
at OwnerNodeTest.start(OwnerNodeTest.java:51)
on IE, the following exception is raised:
sun.plugin.dom.exception.BrowserNotSupportedException: netscape.javascript.JSException: No such property "ownerNode" on JavaScript object
at sun.plugin.dom.DOMObject.getMember(Unknown Source)
at sun.plugin.dom.stylesheets.StyleSheet.getOwnerNode(Unknown Source)
at OwnerNodeTest.start(OwnerNodeTest.java:41)

REPRODUCIBILITY :
This bug can be reproduced always.

The applet source code is:
http://sqeweb/jsn/users/fred/deployment_ws/fred/deployment_6_UR_int_ws/deployment/src/plugin/FunctionalTest/FunctionalTest/src/OwnerNodeTest.java