If you all you need for firefox os apps are: html, css, js then why do I need to add additional cordova library? The big plus of Cordova is you can use HTML5 and write apps that run on other platforms where HTML5 is not natively supported but Firefox OS claims to be HTML5 first.
Cordova seems useless for FireFox OS apps..specially if I'm not using Cordova for any other platform, since performance wise it's not as fast as native on Android/iOS.