It looks very bad to me, doing everything against the UI conventions of the OS. The menu gone from the top right, why oh why? Didn't Firefox success started with being more "native" (close to the OS UI) than the predecessor? The history of bad decisions seems to repeat with every new generation?
Mozilla guys, you really want to annoy your users again? Why?
Australis looks nice in Ubuntu. The new menu is much better with big icons and can be customized however you like it. It's great IMO. I took a couple screenshots from latest nightly release. http://i.imgur.com/19Iwy7r.png, http://i.imgur.com/6Kouk14.png