Prior to JEE5, most developers would bundle a JSF implementation such as MyFaces with the WAR. With AS 4.2 and 5.0, you should instead rely on the JSF implementation that ships with the container.

However, for these legacy applications that rely on a particular implementation, we can disable the built-in JSF implementation as long as you stick with the default classloader settings. To disable the built-in JSF, you will add this to your web.xml:
<context-param>
<param-name>org.jboss.jbossfaces.WAR_BUNDLES_JSF_IMPL</param-name>
<param-value>true</param-value>
</context-param>