Comment 55 for bug 162993

Hm, I'm not sure about the idea of an extra parameter. Its a good idea but it leaves us at the mercy of the image decoder since there is no way in CSS for us to tell which image is being returned.

Because of this, we cannot make new rule declarations to do things like -moz-image-region. Whereas the previous idea with system metrics would allow us to do that and thus not force us to create separate images for every single fallback icon.