It doesn't seems to be using any Chrome api, so porting it to the Firefox SDK should be a trivial matter.

See https://gist.github.com/Spittie/93adf218040d470abd40 (http://81.4.126.121/i/1400019350.png), probably the hardest part is "fixing" the css if it's using some only webkit- feature. Also I'm not sure if it's possible to load local images withing the page-mod api, but embedding them as base64 images is easy enough.

EDIT: oh well, Enjoy: https://github.com/Spittie/octotree No pull-requests because I've moved pretty much everything to make it working. The right way would probably be to use some build system, but who has time for that? :)