From here:
Johan Dahl, 2008-09-01:
A workaround
In gnome: Select System > Settings Sun Java x.x Control Panel
In terminal: jcontrol
- Select the tab advanced.
- Expand the node "Java-console"
- Select show console (default is hide)
Now will the console show up the first time you run an applet. You can keep it open for debugging etc.
If you close the console window must you restart your browser to make it pop-up again.