If I'm judging your screenshot on aliasing/rendering alone, it's very nice (Mac-tier). However, when I look at your screen, I can't help but notice how big everything is on the page. Did you change default font size settings in FF? Could be a GTK issue as well.
Text is being occluded in the red circles; the FB stuff at the top is bigger than it should be; the credits to the right are too big. Here's my FF for comparison, which has the sizes right but bad rendering on the body text:
Screen shot was taken using gnome-core package installed on a CLI Ubuntu 12.04 installed from the netinstall iso. So no Unity desktop. I'm still working out what might be missing or altered in this very non-standard setup.
I'll pop another one on later with a default Unity interface as the Ubuntu team intend
I've always preferred Ubuntu's font rendering over other distributions/oses.
Text is being occluded in the red circles; the FB stuff at the top is bigger than it should be; the credits to the right are too big. Here's my FF for comparison, which has the sizes right but bad rendering on the body text:
http://i.imgur.com/LnY6h.png
And chrome, being even worse with aliasing: http://i.imgur.com/zFcu1.png