[Rodo]

What is this Starfield.pof that people murder children for? 

it's a skybox used to fill up the background of the mission, you see more stars and with more detail with this feature used than without it.

to add it on your missions just type "starfield.pof" in the field "Skybox Model" that you can find in the "Background Editor" (where you put the nebulae).

[Droid803]

And remember to just hit ENTER to close the window and not the X. Sometimes it doesn't save if you don't.
Or something like that >.>