Why does the block height disappear in Firefox if the parent has display:flex?

Question

css

Good afternoon colleagues!
Please, help me solve the issue with the flexbox bug:
SUBJECT: There is a list of items in the flexbox parent. Each item is also a flexbox.
https://codepen.io/emelyanova/pen/mMZLxJ
You need to press the description in the item to the bottom.
For wrapper: display: flex; and flex-direction: column; and margin-top: auto; for description.
PROBLEM: In Firefox, the height of the block with the background image disappears!
In foam - uncomment lines 37-38.
How is it treated?
The prefixes are worth it.
Thank you very much in advance!!!

Answer 1

https://codepen.io/anon/pen/KvjGWx
Block Proportions: https://jsfiddle.net/Ankhena/cLhxv7eq/