Comment by L1quid

For our browser extension, The Camelizer, I wrote Spader: https://github.com/cosmic-shovel/spader

It lets me use Ruby in my html/css/js files, and also sass in the css, letting us use one codebase for all target browsers.

Definitely a work in progress, and lacks the exciting auto-reload functionality of other similar projects, but it works for us. Issuing one build command and having an extension for all our target browsers is pretty nice.