I found a minor issue in 7u15 and 7u21 on Mac 10.8.The steps to reproduce it are:

1. Install 7u15/7u21 JRE.
2. Set security level to Very High.
3. Use firefox to open a JavaFX based JNLP: http://wingding.us.oracle.com/ws/mark/workspace/deployment/src/install/testbase/common/test_apps/BrickBreaker/BrickBreaker.jnlp
4. It will show a warning dialog:
If click "OK" by mouse or by keystroke "space", it will disappear with no problem; but if by keystroke "return", an error dialog "java quit unexpectedly" will show up and generate hs_pid*.log files.

I tried the same steps with non-JavaFX based JNLP: http://wingding.us.oracle.com/ws/mark/workspace/deployment/src/install/testbase/common/test_apps/mg/mg.jnlp
This dialog is not spotted by clicking "OK" in any way.