The Firefox/Help/About Mozilla Firefox can be abit confusing and you will likely find firefox in
/usr/lib/firefox-1.0.4
So, you want to link the java plugin to the firefox-1.0.4/plugins .
Something like this...
Code:
cd /usr/lib/firefox-1.0.4/plugins
ln -s /usr/java/JRE1.5.0_04/plugin/i386/ns7/libjavaplugin_oji.so .