The fix to this very narrow problem is very simple.... before undertaking it ensure that java is working in Safari, that FF is insisiting that you need to install the java plugin (and the plugin is not listed in your plugin window), and that you are running Java 6_33 on OSX 10.6.8 (the solution may address similar issues outside of those constraints, but I have not tested same) - all that confirmed exit FF and go into you profile (likely profile/XXXXXXXX.default) and rename the pluginreg.dat file to pluginreg.dat.bad -- now restart FF and test....
Note that this type of behavior is the result of Java being blocked, and is not pertinent if your java actually starts.