It was the old cartoon that was a take-off on Dicken's Christmas Carol, with Mickey, Donald, Donald's uncle as Scrooge, Jiminy Cricket, etc. During breaks they interviewed lots of celebrities who wished Mickey a Happy 75th Birthday, talked some about Mickey, ate a piece of birthday cake, and showed clips from cartoons during the 75 years. Then back for more Christmas Carol, then break again for more celebrities. It was an hour long. I don't know if it will be shown again since it is on ABC, not Disney channel.
Don't forget to watch the parade at WDW on Christmas morning. I think it's at 10/11central, not sure.