There should be no reason to install from source (that is what nichsmart234 suggested)
There are three ways (all must be done as root):
1. Firefox's precompiled bin file. DL the tarball, extract it, then run the installation wizard. it is just like windows from there.
2. RPM packages. For firefox these are harder to find, but if you look through
ftp://mozilla.org/pub you should be able to find a rpm. The nightly build might have one. DL it then run rpm -U (package name). (There is also a yum repository for those interested, though I can't remeber it's URL)
3. Build from source. DL, extract, gfo into directory, type ./configure, type make, type make install and pray no errors pop up.
I suggest trying them in this order.