Justin D'Arcangelo sent in a detailed article about web servers in Firefox OS: Embedding an HTTP Web Server in Firefox OS.
... we've been looking at harnessing technologies to collectively enable offline P2P connections such as Bluetooth, NFC and WiFi Direct.
The possible use cases enabled by embedding a web server into Firefox OS apps are nearly limitless. Not only can you serve up web content from your device to a desktop browser, as we just did here, but you can also serve up content from one device to another. That also means that you can use HTTP to send and receive data between apps on the same device! Since its inception, FxOS Web Server has been used as a foundation for several exciting experiments at Mozilla.
So it seems like Firefox OS is getting the kind of advanced features that we've seen appear (and in some cases disappear) in Chrome OS, where you get access to native APIs to create desktop-like experiences.
It makes building apps with Marionette more like using the tools you might expect from an IDE, so you should try it out if you already use Marionette or are a Backbone fan that hasn't yet tried it.