I vaguely recall that some or all of the footage was first publicly aired (after it’s single original transmission in 1976) in good quality at some Jim Henson celebration event a couple of years back. Presumably whoever ‘leaked’ this then obtained it from the same source…?
Regardless, although a copy of the episode apparently resides in the Library of Congress the precise status of its preservation had been, until recently, a matter of fierce contention amongst fans.
In the often dispiriting annuls of missing and lost footage a happy resolution for once then!
Update: The Library of Congress has issued a statement confirming the leaked episode was indeed obtained from them, illegally. The identity of the culprit and the circumstances of the theft remain undisclosed but take down notices have begun to be issued so those who still wish to see the episode should hurry ‘coz they’re going fast!