I am working with images, and I ran across a problem with aspect ratios.
There is no standard way to preserve aspect ratio for images with width, height and max-width specified together.
So we are forced either to specify width and height to prevent page “jumps” during loading images, or to use max-width and not specify dimensions for images.
Specifying just width (without height) typically makes not much sense, but you can try to override the height HTML-attribute by adding a rule like IMG {height: auto; } into your stylesheet.
See also the related Firefox bug 392261.