Mozilla will be rolling out the stable version of the Firefox Australis (Ff 29) next Tuesday.
If you don’t like it, there’s an extension called Classic Theme Restorer (imaginative name, eh?), which can be found here.
If you want a good explanation of differences and some features of Australis, you can find them here.
There’s another add on: The Fox, Only Better which changes some interface elements but is a lot truer to Australis in appearance.
Anyway, just ...