The 'old' NS images are the original images supplied with the Joust system, when the core Mozilla browser was Netscape.  Now that the core browser is Firefox, I've updated the images.  
I'm sure there will be some sub-field that would allow you (in index.htm, around about line 928) to differentiate between these two browsers, but life's too short...

Colin Millerchip.
10:42 10/07/2005