After first reading through the FC rulebook, I came to the conclusion that natural 20s and natural 1s weren't treated specially as they are in e.g. D&D. Nowhere in the standard attack, or skill check sections do they mention them.
In the places where they mention errors and threats, it specifically calls out that for it to be an error or threat, the roll must have succeeded.
So, I've been playing that way for a while, but then someone pointed out the following sentence on page 361 of the rulebook:
Statistically, 5% of all rolls fail (with a natural 1), which makes sense in isolated situations — especially dire, desperate ones.
I fired up the PDF version and found all occurrences of the word "natural" and found that to be the only place in the rulebook speaking to treating natural 1s or 20s specially.