I can confirm that FF3 and Java6 works at Hardy Alpha 6 only after applying both proposed solutions:
$ sudo sed -i 's/XINERAMA/FAKEEXTN/g' /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so
$ cd /usr/lib/firefox-addons/plugins/
$ sudo ln -s /etc/alternatives/firefox-3.0-javaplugin.so
I can confirm that FF3 and Java6 works at Hardy Alpha 6 only after applying both proposed solutions: FAKEEXTN/ g' /usr/lib/ jvm/java- 6-sun-1. 6.0.04/ jre/lib/ i386/xawt/ libmawt. so firefox- addons/ plugins/ es/firefox- 3.0-javaplugin. so
$ sudo sed -i 's/XINERAMA/
$ cd /usr/lib/
$ sudo ln -s /etc/alternativ