This is an example alternatives install line.  Note the firefox plugin.

/usr/sbin/alternatives --install /usr/bin/java java /usr/java/jre1.6.0_26/bin/java 120 --slave /usr/bin/keytool keytool /usr/java/jre1.6.0_26/bin/keytool --slave /usr/bin/rmiregistry rmiregistry /usr/java/jre1.6.0_26/bin/rmiregistry --slave /usr/lib/mozilla/plugins/libnpjp2.so mozilla-javaplugin.so /usr/java/jre1.6.0_26/lib/i386/libnpjp2.so