Download firefox package and move it to /opt directory

[root@www ~]# cd /opt

[root@www opt]# ls
firefox-13.0.1.tar.bz2

[root@www opt]# tar xvjf firefox-13.0.1.tar.bz2

[root@www opt]# ls
firefox         firefox-13.0.1.tar.bz2
[root@www opt]# cd firefox

[root@www firefox]# ls
application.ini             jssubloader       libssl3.so
blocklist.xml               libfreebl3.chk    libxpcom.so
chrome                      libfreebl3.so     libxul.so
chrome.manifest             libmozalloc.so    mozilla-xremote-client
components                  libmozsqlite3.so  omni.ja
crashreporter               libnspr4.so       platform.ini
crashreporter.ini           libnss3.so        plugin-container
crashreporter-override.ini  libnssckbi.so     precomplete
defaults                    libnssdbm3.chk    removed-files
dependentlibs.list          libnssdbm3.so     run-mozilla.sh
dictionaries                libnssutil3.so    searchplugins
extensions                  libplc4.so        Throbber-small.gif
firefox                     libplds4.so       updater
firefox-bin                 libsmime3.so      updater.ini
icons                       libsoftokn3.chk   update-settings.ini
jsloader                    libsoftokn3.so

Remove older firefox from /usr/bin/ directory

[root@www firefox]# mv firefox /usr/bin