Easy Futurama X-Mas song question

Cafe Society
1

In the second X-Mas show, “A Tale of Two Santas”, the newly-liberated Neptunian pseudo-elves sing as they go back to work:

We are free and fairly sober
With so many toys to build.
The machines are kinda tricky
Prob’bly someone will be killed…
What’s the song being spoofed, here? I can find the lyrics easily enough, but nobody seems to cite the title of the original song.

2

I think it’s a Futurama original

3

Huh. For some reason I thought they were using an old-standard melody.

4

Ken Keeler has both music and lyrics credits on this song - so I’d guess it’s original.
http://www.imdb.com/name/nm0444517/