I'm not sure what you're asking. File extensions are relatively meaningless, and the *default* file extension depends on which version of JSF you're using. You can decide which view technology to use based on your needs, core competencies, and so on.
JavaServer Faces (JSF) technology is a new UI framework mainly used for J2EE applications with MVC architecture. JSF clearly defines a separation between business logic and presentation while making it easy to connect the presentation layer to the application code. You are right when you say that JSF is MVC based.
As Bart Kummel as pointed out in one of your previous posts the file extension for a jsf file is configurable as per your wish.
You can even use filename.jsf but you have to first configure the extension .jsf to be parsed as a specified in the code by Bart. You will just have to change *.xhtml to *.jsf or any other extension you like.
With JSF you have the option of using Facelets or jsp for view component but facelets is preferred as it is a relatively new technology and much better at separating the business logic from view components.
Also you can use PrimeFaces, RichFaces, MyFaces etc which are jsf component providers and they are open source.
Even i am new to JSF but believe me you'll start liking it before you even know.