I was just googling the song & found this thread. I know the thread is old, but here's what I remember

Oh Christmas is i-come
Mark ye robin's ruddy tum
and the wind it e-bloweth very rough, rough rough

Now do as ye be told
and keep us from the cold
and fill us up with figgy figgy duff
figgy duff!


I learnt this in school 30 years ago!
:)