OSX sub-pixel anti-aliasing can make fonts very bold. This seems to be the problem here.
Take a look at this blown up snapshot of the text you posted:

See what color crop your text? This is sub-pixel smoothing.
What you can do is disable it using CSS:
.yourtext { -webkit-font-smoothing: antialiased; }
As you can probably learn from the -webkit provider prefix, this will only work for Safari and Chrome. There are hacker methods for disabling subpixel anti-aliasing in Firefox for OSX (e.g. opacity: .99 ), but I don't know if this is a good idea.
I am a little surprised that Fonts.com does not know about this, especially since they themselves disable sub-pixel anti-aliasing.
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