P.S. Screenshot: http://imgur.com/m4rLSHQ
P.S. Screenshot: http://imgur.com/m4rLSHQ
[Edit:] Those ultra-light fonts are a very unfortunate fad that probably began with the introduction of iOS 7, maybe even earlier with MS's Metro, contrived and perpetuated by people who don't read but who look at texts.
On Firefox, Alt-V Y N (for no style) is in muscle memory by now, and renders in glorious 1990s black and white, and the text flows within the browser borders (another problem on many sites today).
My current settings are: Medium and Grayscale respectively. (on Gnome Shell)
What Linux are you running? "fc20" I guess that's Fedora? So it looks bad on Firefox on Fedora but fine on Ubuntu. That's a Fedora issue not a Firefox or general Linux issue.
Based on the other comments I got, the small differences could be caused by different anti-aliasing settings or font engines (I'm currently using freetype-freeworld-2.5.0.1-5 for example).
PS I agree too, they look better in Chrome, don't know why.