Comment 4 for bug 511151

Harry's solution worked for me. To make it easier, these are the commands that did the trick for me (use at your own risk!)

sudo rm /etc/alternatives/mozilla-javaplugin.so

sudo ln -s /usr/lib/jvm/java-6-sun/jre/lib/amd64/libnpjp2.so /etc/alternatives/mozilla-javaplugin.so

sudo rm /usr/lib/mozilla/plugins/libjavaplugin.so

sudo ln -s /etc/alternatives/mozilla-javaplugin.so /usr/lib/mozilla/plugins/libjavaplugin.so