XP: I just updated to firefox 3.6.3 and Java is gone, apps don't run. The Java affordances are gone from Options. Do I download Java from somewhere? Can I roll back to a firefox version that was working?
Open firefox and select the Tools/Add-ons/Plug-ins and see if the Java plug-ins are disabled. If so, click on enable and restart firefox.
If, for some reason, the Java runtime has been corrupted, you can download the most recent version from here:
Alternatively, you can download JavaRa a small utility that will allow you do remove any old versions of the JRE left on your PC and also download the latest version.