Well,
I noticed the following:
* The ANIM tag has some crypto stuff there.  This is something that
  Netscape only wants their own web pages to control.
* There was another web page with a modified animation of the Mozilla
  creature coming up and breathing fire.  Also a Netscape web page.
* Netscape changes what this logo does in OEM packagings of Netscape
* The animation is in the Netscape binary, and not downloaded from the
  web page.  There are probably only a couple other Animations in the
  binary (the fire-breathing Mozilla being the only other one I have seen)
* I vaguely remember people talking about finding the standard animated
  sequence in the Netscape binary and changing it.  Sounds like an
  alt.hackers thing.
- Sam
-- 
"You can...turn sadness into laughter" -- Sunscreem, _Love_U_More_
Ignore my last posting.  The ANIM tag is purely bogus.  Instead, what jwz
did was hardcode Netscape to change the animation if you choose the URL
http://people.netscape.com/jwz.  This was verified by me changing
/etc/hosts to have people.netscape.com point to my own machine.  The jwz
URL gave a 404, but the thingy in the upper right hand corner became the
spinning compass.
The fire-breathing Mozilla was probably similarly encoded.
- Sam
More info:
http://looney.physics.sunysb.edu/~daffy/jwz/cool.html