Firefox 2.x / Linux image scaling

Why does image scaling seem to be so bad in Firefox 2 on Linux?

For one of our web apps we want to show static pixmap images of chemical depictions. Depending on the context we want to show those depictions at different sizes, and we don't want to create and cache too many renderings. We'd rather create one fairly large rendering and have the browser scale it down as needed.

For users who are running Firefox/Win or Firefox/Mac this works fairly well, if the images aren't scaled down too much. (Otherwise lines get too thin, as you'd expect.) But for Firefox/Linux users, the results look horrible.

ff_mac.png ff_linux.png
Firefox/Mac Firefox/Linux

What's up with that? Is there any way to control how Firefox downscales images, to get better quality?

Perhaps not. Or not yet, at least. Acts of Volition has an entry comparing image resizing in Firefox 2.x and Firefox 3. Paraphrasing:
The Cairo graphics library will power Firefox 3.
In Firefox 2, if you tell the browser to resize an image it will do so, but not with any of the smoothness that you would see if you had resized the image in an application like Photoshop or the Gimp.

Now, in Firefox 3.0 Alpha 1, resizing an image like this actually produces a smoothly sized image.