Difficult to explain problem with full page zoom in Firefox

I use Firefox and it look that it has got some strange problem with full page zooming.

When I zoom out images develop a blackish outline around them which looks ugly. However on zooming >= 100% the problem disappears.

What should I do to avoid this problem.

Image with zoom < 100%
*img13.imageshack.us/img13/9823/problematj.jpg


Image with 100% zoom
*img83.imageshack.us/img83/6883/nproblem.jpg