Well, time to eat some humble pie. First off, I'd like to thank Dan (zelph) for bringing up the idea of having higher pot supports, and that this might explain what Chris Martin described (see FireFly puzzler posts above this one). Dan has lots of stove experience, and I'm glad he took the time to make his observations, as I believe the growing number of FireFly users will benefit from them.
Anyway, this being a non-working, non-hiking weekend for me, I thought it would be a great time to do some backyard testing of Dan's hypothesis. I did numerous burns this morning using found twigs from my backyard without any special preparation. I have come to 4 conclusions:
(1) If you are using a tall cooking mug, a beer can pot, or something similar, the regular height of the FireFly pot supports (3/4 inch) works just fine.
(2) If you are using a fairly large pot with a big bottom diameter, like a squat 1.3L Evernew pot, higher pot supports definitely work better (less smoke, better burn and heating of pot).
(3) If you are using something in a middle size range, like a squat 900 ml pot, you will probably also prefer higher pot supports, though you may decide that the regular height works just fine for you. Tall 900 ml pots work pretty well without them.
(4) If your goal is to have a longer burn with little smoke, lighting your fire from the top is definitely the way to go.
The FireFly, fortunately, was already designed with and shipped with small pot supports for narrow/tall cooking mugs, beer can pots, and the like. This made it easy to come with (drum roll) "large pot supports" that are attached the same way, and raise a pot an additional 1.25 inches. Time for a photo:
So for those of you who have a FireFly, including Chris (if I can get his mailing address), I will send you on request, at no charge, a pair of these large pot supports. For those of you thinking about getting a FireFly, these large pot supports will also be included as part of the basic package. They go easily into your tyvek pouch with the stove.
For a video showing a top down burn with a large pot and the new supports (as well as boiling 3 cups of water with one stove-load of wood), see: