Remove the plugin link manually - if your Mozilla lib directory is /usr/lib/mozilla then your plugins directory should be /usr/lib/mozilla/plugins. In that directory you should find a symbolic link called libjavaplugin_oji.so. Remove it and create a new one, pointing to the plugin object file in the ns610-gcc32 subdirectory of the JRE plugin installation:
to the Mozilla plugin directory, then create the new symbolic link: ln -s /usr/local/java/j2sdk-1.4.2_04/jre/plugin/i386/ns610-gcc32/libjavaplugin_oji.so .
The path above will most likely be different from yours since it seems I am the only person alive using /usr/local/java for installing Java related stuff.