How do i use a Java Runtime Environment plugin in Firefox?

On the Fedora Linux machines, you should be able to do that
by creating a directory ~/.mozilla/plugins, and in that
directory create a symlink :

cd ~/.mozilla/plugins
ln -s /usr/local/jdk/jre/plugin/i386/ns7/libjavaplugin_oji.so .

Then exit and restart Firefox.

Note:  The Linux Java Runtime Environment plugin appears to work only with 32-bit versions of Firefox. On 64-bit machines such as graphicsXX in GS930, the JRE plugin does not work with the default version of Firefox (/usr/bin/firefox) since it is 64-bit.

A workaround is to use the JRE plugin with a 32-bit version of Firefox.  A 32-bit version of Firefox is installed on the graphics machines in /usr/local/bin/firefox32.