Q:

jpg looks different in firefox 6 and 7 on Windows 7

This website renders a background jpg differently than it did in Firefox 5 and below on Windows 7.  I know that's a bit confusing so I'll outline it.
It works:
All versions of firefox, chrome, and IE on windows XP
All versions of chrome, IE, and firefox 5 and below on windows 7
Example:

It doesn't work:
Firefox 6 and above on Windows 7
Example:

The website is repeating the gradient jpg horizontally.  It then tries to make the background color the same color as the bottom of that gradient.
Thanks again SO.

A:

On my Windows 7 / FF6, the gradient looks pretty smooth:

so I think that what you're seeing is machine specific.  
However, you might have better results by using a .GIF with a transparent bottom (to fade to background color) rather than a .JPG.  In general, you've got better control over the colors in a .GIF because it's not a lossy format if you have few enough colors.

