Would like to have this effect on one of my pages.

Have tried using this tut:

HTML5 Grayscale Image Hover

But getting mixed results on my MAMP setup. i.e. Firefox and Chrome not showing at all. Safari only shows the colour image on hover.

There is a note suggesting this may be the case in a local set up - why would this be the case? I'm kinda weary rolling it out live only to find it's still not working.

Is there a better method/tut that anyone could suggest/post?

Grateful for any replies.