calls from JDK9 or later JDK8 deployment code to showBlockedDialog() result in a AbstractMethodException when run with JDK7 or JDK8 before 8u20.
This method in com.sun.deploy.uitoolkit.ui.UIFactory should be made non-abstract, and some default implementation should be used.

you can see this installing JDK9 and 7u80 then run: 
http://oklahoma.us.oracle.com/www/tests/dialogs/jnlp/fx7.jnlp
look at 11: showBlockedDialog()