Via the Xbox 360 console, you are unable to view the public friendlist of a friend's friend. This means that if you view a friend's friendlist, select the profile of one of their friends, the option to "View Friends" is removed. Even if their friendlist is public, and even if the friend is on your own friedlist as well. This limitation does not apply to xbox.com, only the Xbox 360 console.
Is this intentional, or a glitch in the service? I recall being able to do this long ago, after the NXE update, but have had no need for this feature until now.