Firefox 3 displays pieces of desktop background

[Mark Kirkwood]

I'm on 7.1 Prerelease refreshed a few days ago. I've noticed that 
Firefox 3 (3.0.4, but 3.0.3 was the same) displays snippets from ones 
desktop on some webpages (yahoo and youtube being the 2 most recent).

I've tried to get together a simple test page to illustrate what is 
happening and put it here:

http://homepages.paradise.net.nz/markir/test.html

This should display some text on a grey background (which it does in 
Epiphany for instance). However in Firefox 3 it uses my desktop 
background as the web page background in some strange way. Any ideas?

regards

Mark