This Firefox addon contains full-featured console that supports JS, CoffeeScript and LiveScript.
Info and screencast are available at http://paulrouget.com/e/jsterm/.
To switch between languages, use :js, :coffee & :livescript.
The language you choose will be saved for the next console session.
Screenshot:
Drag’n’drop .xpi on your Firefox.
If you prefer stable versions, you can install the addon from addons.mozilla.org.