Help needed from Mac users

[wac]

I've been informed of a fault with one of my sites but being that I'm unable to replicate the issue, it's making it difficult to fix.
http://www.ppsprint.co.uk/folders.html
On the above link, I'm told that if your using Firefox on OSX and you try and and scroll up and down (without using the scroll bar arrows) that the box goes black.

Is anyone else experiencing this issue or does anyone have any idea what the problem might be.

 

[Tony Hardy]

Also unable to replicate the issue here. Everything works no problem on Firefox on OSX at this side.

 

[si_p]

Just tested on FF and I can't force the error. Tried scrolling normally, using the fn+arrow keys, and via the tablet. Frame scrolls smoothly each time.

 

[Jimlad]

No problems here either, running Firefox on OS X Snow Leopard. Maybe its a Lion issue?
[Edit] No problems in Mountain Lion either.

 

[wac]

A mystery then, thanks anyway chaps.