My favorite of all is this one. Dark so you can see your tabs. Subtle animation so as not to overload your eyes. Light and dark contrasts. Just lovely!

Lovely looks, easy to use and see all the functions of Firefox. One con though, after a while the animations stops and the butterflies stay static forever after that.

It's simple, but the movement of the butterflies wings adds an elegant feel to it.

Love the Butterflies