To setup java plugin for Firefox

Env:
64-bit Fedora 12 Constantine
Firefox 3.5.9
java version 1.6.0_18


before execute

sudo /usr/sbin/alternatives --install /usr/lib64/mozilla/plugins/libjavaplugin.so \
libjavaplugin.so.x86_64 /usr/java/default/lib/amd64/libnpjp2.so 20000

as shown in http://www.mjmwired.net/resources/mjm-fedora-f12.html#java

try
ls /usr/java/default/lib/amd64/libnpjp2.so

and make sure the file exist

for me, libnpjp2.so resides in

/usr/java/default/jre/lib/amd64/libnpjp2.so
not
/usr/java/default/lib/amd64/libnpjp2.so

so change the command to the correct path:

sudo /usr/sbin/alternatives --install /usr/lib64/mozilla/plugins/libjavaplugin.so \
libjavaplugin.so.x86_64 /usr/java/default/jre/lib/amd64/libnpjp2.so 20000