Addendum... or Part Five (of Four)
During the making of the movie, the Henson people had constructed these chairs for puppeteering from the floor. Basically, they were plastic seats with the legs removed, then mounted to metal frames with four coasters on them. The seat backs could be tilted and locked in place at three different angles. The last being, almost laying on your back with your arms straight up in the air.
Anyone who has tried to sit on the floor and hold puppets over their heads for any length of time will know what stress this puts on your back. Using the chairs, which give you back support, you are able to puppeteer for long periods of time without being uncomfortable. The wheels also make it possible to move around with your feet so your puppet can "walk". Or, someone else pulls you via a line attached to the front of the metal frame.
The chairs were used extensively in "The Magic Store" song.
About a year after production was finished on the film, there was an auction of all the props and costumes from the movie. They had all the vehicles including Fozzie's car and the Electric Mayhem bus. But there were two things that I was particularly interested in (and even had a hope of being able to afford). One was the stool that Kermit sat on. This was not a radio-control puppet. Instead, it's an old magician's trick and an ingenious prop. It's a three-legged stool with a hole cut in the center of it. You position the stool so one leg is out front and two are on the sides. Then, there was a mylar mirror between the two side legs. The camera was positioned in such a way that the reflection of the front leg created the rear leg. In reality, Jim was crammed behind the mirror operating Kermit. My friend wound up winning the stool. (Side note: we were actually able to recreate the effect at home using a video camera!)
The other items, when they came up, the auctioneer didn't even know what they were. They went as a lot. The three puppeteer chairs. I won that auction! I still have them in storage and have actually used them for puppeteering on TV. Because of the added comfort, I could work all day in them, where in the old days of sitting on the floor, I would have been wrecked after ten minutes without long breaks.