I downloaded firefox-22.0.tar.bz2 and Firefox 22 is now installed in /usr/local/firefox. I did not follow the official Firefox guide for installing on a Linux system, where installation to /home/userID/firefox is recommended. I had seen installation to /usr/local/firefox described as "the right way" to install Firefox, so I followed that procedure.
There were no problems installing Firefox to /usr/local/firefox, and I'm now using it daily. I did not delete the older Firefox version that is bundled with the Slitaz 4.0 Firefox distro (stable), so I can easily revert back to it if the need arises. Retaining the older Firefox version, however, made it necessary to add /usr/local/firefox to my PATH by editing /etc/profile. The directory /usr/local/firefox is first in the PATH, making ASH find and run the Firefox 22 binary first, rather than the older Firefox binary. I also did "chmod 755 firefox" to the Firefox 22 binary (/usr/local/firefox/firefox), and Firefox 22 runs when I click the desktop menu item as normal user.
I installed Slitaz 4.0 Firefox (stable) in January 2013, but did not begin using it until July 2013. It is installed on a very old Compaq Deskpro EN, Pentium III 933 MHz, 512 MB RAM, 20 GB HDD. The monitor is a 17-inch HP L1720. The install of Slitaz 4.0 Firefox was fast, easy, and without any problems. Performance on the Pentium III is amazing. A very compact distro, but very powerful. I had previously used Mandriva Free 2007 and PCLinuxOS LXDE 2009, 2010. Slitaz 4.0 Firefox is superior to those other distros in overall simplicity and design quality. Dial-up connection to the Internet is through a USRobotics USB modem (model USR5637).
Thank you Slitaz developers for a job well done.