Chrome and Firefox uses two different scaling algorithms that is probably contributing a lot more to this difference. Chrome is more blurry in general while Firefox is sharper but has slightly more ringing artifacts. Personally I prefer the Firefox version.
I do prefer the firefox look too! I'd be curious to hear your take on what could be the root cause of this. I'm far from a image rendering expert. But I remember when inspecting the edges and curves of the images in a DCT visualizer they were all in the AC coefficients which is what led me to the conclusion of the post.
I've noticed that a lot of objective measures of image quality prefer blur to ringing, but many subjective measurements tilt the other way.