The earliest iterations of Australis design concept are dated back to more than 2 years ago, when it was just a simple mockup, made for discussion purposes in order to explore different design directions. Back then it looked something like this:
Nowadays, the project has matured a lot and finally took shape, after it had been through some comprehensive refinements, and also got a new customization framework included (see below). It is currently available as a nightly version of Firefox, that is to say soon to be released as a stable version.
Download & Install
In case you’re interested in giving it a go, it is presently available for download as a binary from here, you have no need to install it, just unzip the tar file and launch Firefox from its directory. Note, you must close your current running Firefox for it to work, since both use some shared configuration files.
Finally, check out the following video to see the intro of Australis and a demonstration of it.