Why is the block displayed incorrectly in Mozilla?

Question

css

Hello. I ran into a problem: idontcare.zzz.com.ua
In all browsers it normally shows (in the center), and in Mozilla a block at the top initially appears, but when resizing the window, at least 1 pixel in any direction, it falls into place. What can be funny?

Answer 1

Do not use crutches in the form of a fixed width and height, and then margin.
Do this:

div.section.fp-section {
display: flex;
flex-direction: column;
}
div.section.fp-section>* {
margin: auto;
}

Selectors, of course, insert your own.