It is always recomended to use the yum to install any package right grom the fedora repository. However, if one like to install Firefox 2 using firefox-2.*.tar.gz from Mozilla.com then you can follow this instruction. One benefit of this option is that Firefox 1.5 remains on your machine so have a choice as to which version to run.Instructions (as root):

Download firefox-*.tar.gz from Mozilla.com.

# mv firefox-2.*.tar.gz /usr/local/
# cd /usr/local
# tar xvfz firefox-2.*.tar.gz
# mv /usr/bin/firefox /usr/bin/firefox15
# ln -s /usr/local/firefox/firefox /usr/bin/firefox