Using the Awesomium Mac SDK.
http://awesomium.com/download
http://wiki.awesomium.com/getting-started/setting-up-on-macosx.html
How do I get a C2 game to run on Mac?
As far as I know, awesomium has yet to implement mac support though they have announced they'll be implementing it.
It has mac support.
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I'm guessing that Ashley just hasn't implemented it yet, then.