Comment 31 for bug 112994

Had this problem in the gutsy final release, but the solution above didn't work.

To fix I had to update the symbolic link /etc/alternatives/firefox-javaplugin

Old Incorrect location: /usr/lib/jvm/java-1.6.0-sun/jre/plugin/i386/ns7/libjavaplugin_oji.so
New Correct location: /usr/lib/jvm/java-6-sun/jre/plugin/i386/ns7/libjavaplugin_oji.so

Seems that if you had java 6 installed in feisty, then upgraded to gutsy, this got broke. Installing the plugin via firefox didn't help, since that only points to the alternatives link, which was pointing at a nonexistent java.

Hope this helps someone else whose still trying to get the java plugin working after update...