yum install firefox
yum update firefox
NOTE: YUM is the recommended mechanism for installing packages
If for some reason you cannot use yum then...
Using the current version of Firefox on OEL...
Download latest Firefox from Mozilla web page...
https://www.mozilla.org/en-US/firefox/desktop/
Then, as root, in the directory you downloaded to...
tar -xjvf firefox-17.0.tar.bz2
cp -r firefox /opt/
ln -sf /opt/firefox/firefox /usr/bin/firefox