Firefox has its own font rendering, it displays horribly with retina scaling. See for example http://media02.hongkiat.com/mbp-retina/chrome-vs-firefox-vs-...

It may seem picky, but its very obvious when browsing.

That screenshot looks less like "Firefox displays horribly with retina scaling" and more like "everything other than Safari displays horribly with retina scaling."

Which Apple may consider a feature rather than a bug :-D

It's an old screenshot from before Chrome got Retina support.

That picture doesn't do it justice, Chrome looks significantly better than Firefox.