More information on this browser release can be found in the Slashdot article linked above, or in the press release.
Tip: I found it easiest to extract the Firefox tarball under /usr/local. From the Toolchest, select Desktop -> Customize -> Utilities. Under Web Browser select Other, type /usr/local/firefox/firefox in the dialog box and click OK. Now you can run Firefox by selecting Internet -> Open Web Browser from the Toolchest. This will help integrate Firefox into the desktop so elements such as WebJumpers and InfoSearch work as expected.