cordova-firefoxos allows developers to use the cross platform APIs in Cordova to target the Firefox OS. Most APIs are just proxied to the matching Firefox OS API calls.
There are no prerequisites for adding Firefox OS as a Cordova platform. For usage, setting up debugging environment and running on the device, see the Cordova support for Firefox OS page on Mozilla Developer Network.
For platform development information, check out the Firefox OS cordova development page
A lot of good documentation on Firefox OS development is also available on the Mozilla Developer Network.