I just upgrade my firefox version to 3.6, in the beginning as usual some of my add-ons do not work, but eventually they will, no problem at all except when I try to use the java plugin I make a little research at mozdev site and found a change in the plugin path:
/usr/java/jre1.6.0_18/lib/i386/libnpjp2.so
This is the new file that must be like a symbolic link at plugins directory into your firefox version, this resolve the issue of no java plugin installed.