Firefox bug 674373 has landed;Â Firefox nightly builds now natively support the Retina MacBook Pro display!
It also now supports the window.devicePixelRatio interface which my in-progress high-DPI image support for MediaWiki uses to determine which resolution images to load. It looks great on my Retina MacBook Pro! This should land in the final Firefox 18 release in a couple months for those not on the bleeding edge of the upgrade treadmill.
Unfortunately there’s a bug which causes window.devicePixelRatio to report an incorrect value on Android, so hi-dpi support for Firefox mobile is slightly broken pending bugs 794056 and 779527.