Firefox OS could host nodejs app's in an offline mode? Just like a normal app just because it uses only HTML5 (till today) form deploying app's to this new plattform.
Or the new system uses only apps as webservices like normal html does?
If I understand your question correctly, if you mean creating and hosting a web application in Node.JS, and using that same web application when offline, then the answer is yes.
You should look into what hosted applications are and enhancing your application with offline capabilities by using the cache manifest for caching application resources and using the browser/local storage for storing application data for offline use.