If you are sure that you have a 32bit version of Firefox installed, it should really be easy. The repo is already setup, if you did the tutorial setup ..
In a Command line console, just
yum install flash-plugin.
yum info firefox
should only return one instance of Firefox...
this work for me every time. If not....
SmotlSendProfile.... paste the link here, and then we know what you have on your box.... maybe the help will then be a bit better..