[CentOS] How to configure xguest Firefox home page

I've installed CentOS 6.6 on a workstation at a local non-profit as a
kiosk machine. I used xguest.  Works great, except now the customer
wants the Firefox homepage to be one pointing to a particular site.
Doesn't seem to be much documentation on how to make minor changes to
the account. Lots of SELinux guidance, but nothing about default home
page, etc.

Dave