Zen Wood II | by Mr.Cline nga Mr.Cline

The cooler version of a rather dark, natural, wooden theme with a green accent.

Check out Version one as well!
https://addons.mozilla.org/en-US/firefox/addon/zen-wood-by-mr-cline/

You find more natural wooden themes here!
https://addons.mozilla.org/en-US/firefox/collections/15195387/Wood-Textures/