Firefox's Problems
Firefox as of version 1.5 includes its own SVG implementation called Cairo as part of the browser. This is a great development for SVG but many SVG features used in this tutorial have yet to be added to Cairo.
For more information about the limitations of Cairo: SVG in Firefox 1.5 (external link)
Work Around
To use the Adobe SVG viewer with Firefox follow these steps. (Mac OS X)
Windows Firefox users also have to use Adobe SVG Viewer 6.0 and move the SVG plugin from its install location into Firefox's plugin folder. See Mozdev.org.
All the examples will now work. Please contact me if these instructions don't work for you!