on my website i have a menu that when you rollover an image it is replaced with a .gif animation. on firefox all frames are played, but on ie8 it skips straight to the last frame. you can see this here:
I'm not overly sure of why this may be the case, but you could try using a css :hover attribute as a method. I have a feeling it may be to do with the images being pre-loaded, but I'm not sure about this.
It's because he has used a JS script from Dynamic Drive that is not sufficiently robust cross-platform. There are many jQuery plugins for menu transition effects that would be much more robust and just as easy to implement.
(Incidentally, :hover is a pseudo-class, not an attribute. Attributes are used in HTML.)