Above you see an PNG image with alpha channel stretched vertically longer than the original image size. Scrolling with the page with such images seems to have some paint bugs with Mozilla (0.9.8 at least).
  1. Scroll the page down a bit so that you don't see the image anymore.
  2. Grab the scrollbar and scroll very slowly back to top of the page (try to do it pixel by pixel). For me the image looks like this after that:
The bug is visible only in the portion of the image which has some transparency (i.e. image blending value is less than 100%).

Tested on platform:

Operating System
Win2000
Mozilla Version
0.9.8
Screen Resolution
1152x864
Screen Depth
32 bpp