Could you write more what is wrong with firefox on this screenshot?
I don't know if you're being hyperbolic, but that feels like a really minor thing to me.
Direct comparison of some of the more egregious examples in Firefox (Top) vs Chrome (bottom). Look at the tab title, the text in the dark grey nav bar, the aliasing on the back button, the aliasing on the text, the aliasing on the edge of the "O" in the Google logo, and the aliasing of the text under the buttons.
I'm not sure what they could have done beyond making sure Cocoa's text-rendering routines produce the right "retina" output. Which they do. Firefox (and Chrome) do their own text rendering and rasterizing, as far as OSX can see it they give it a big image to display. Not much OSX can do with that.
Left is Firefox, right is Chrome. Nothing special done to either. MBP is at the factory resolution. Very ironically, the screenshot at half-size looks better on my 24" Windows display than it does on the actual MBP does, presumably as Chrome is doing some resampling to downsize it. Look at it at full zoom to see what I mean.
I'm doing active web development on a number of browsers across a number of devices (Macs, Windows, iOS, Android), and Firefox on the Mac is easily the worst of the lot, by a rather large margin. I would easily notice if the whole screen looked like it - text is blurry and awfully aliased, to the point that it's jarring to read. I spend most of my time on Windows, which by most accounts has less beautiful text rendering than OS X, and switching over to Firefox on the rMBP feels just awful.
Given that I spend 99% of my day looking at a 94 DPI screen, I don't think it's too much to ask that the same application on my 220 DPI display not look like I'm playing Minecraft.