uninstalling sun java plugin for firefox is easy with these commands i have used in a fedora linux server i have for testing, these are the steps i took to remove java

login as superuser


check to see what version you have installed in your linux:
rpm -qa | grep jre

output: jre-1.6.0_19-fcs

since i have installed: jre-1.6.0_19-fcs this is how i remove it

rpm -e jre-1.6.0_19-fcs

this is the output i got:

Preparing packages for installation...
You have mail in /var/spool/mail/root