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 to keep you Firefox users up to date…by the way, with the new IE exploit, changing to Firefox is certainly a way around it.
Sources for this are in the links above.