Firefox new theme (Australis) Has been planned since Firefox 4 (2010)
https://wiki.mozilla.org/Firefox/Features/Theme_Refinement_and_Evolution_%28Australis%29
And I can say that Firefox new theme looks better than chromes:
http://i1.minus.com/iybdzewkakjg.bmp
ANDDD if you dont like the minimalist look, Firefox allow you to change that by yourself:
http://i3.minus.com/ibtdeEaLoSnps8.bmp