It's a little cheezy but also really cool to see an animated theme on firefox. Also I like how it fades fairly quickly into a solid dark color. That improves visibility a lot and the fade off is well handled.
I'd give 5 stars if the colour of the tab names weren't so similar to the pink flowers of the trees on the right side. It makes using the browser more difficult, cause you can't see like half of the tabs you've opened. Maybe white would be better?