Hi @dansmister-at-gmail-com, great question!
It isn't LIFO, as the app calculates the time when to reinforce the words, based on your answers. Those words which you make more mistakes in, you will see more frequently. And those words, which you are doing well with, you won't see for a while.
Whatever the algorithm your using, I am very impressed. It feels like I'm playing a game, and when I play well, I get rewarded with a new word -- and this happens often enough to keep my interest, but not so often that I get saturated. Keep it up and Ill send you some real flowers.