For a variety of reasons, my dwarves are descending into madness, and my FPS rate is 1/10th of what it normally is. It's making my sweet fortress really hard to play.
This isn't a question, and would probably fit better in DF Mode or DF Questions if it were, but regardless:
Madness:Madness can be hard to counteract, but the usuals of giving them nice bedrooms, a nice dining room to eat in, etc. always help, especially if things were sort of dreary or haphazard before.
As a more severe, probably harder to enact solution, you can try locking grumpy dwarves in isolation so that they can recover without assaulting others, thereby stopping the spiral. Obviously, this works a lot better when it's just a handful who are upset than when your entire fort is angry at each other, but even then fewer dwarves to go berserk on each other is probably a good thing. Remember that tantruming improves their mood, so every tantrum without further injury is progress.
FPS:Many, many things affect FPS, but stray items are one of the most serious. If you've got a lot of stray items- raw stone, clothing from the deceased, etc.- consider trying to clean them up. An atom smasher bridge or magma can dispose of most items, and/or you could give your dwarves cabinets to store their spare clothing in.
What is the function of a window? I have an artifact window made of dematoid and I want to know what to do with it.
It's probably extremely valuable, and can thus improve the value of a room. That's mostly it, though I believe there's a handful of very specialized, mostly deranged uses for its see-through-but-solid nature.