It's important to be mindful of what you are trying to accomplish here.
The issue may lie in instructing the child element to have a position absolute with 0px on all four sides, leading to differing interpretations by different browsers. This lack of specificity regarding width and height can cause discrepancies in how Chrome and Firefox display the element.
In Chrome, the browser seems to default to setting the child element's dimensions to match those of its parent (100% width and height), as evidenced by inspecting the computed styles.
On the other hand, Firefox does not automatically assign height or width to the child element, resulting in it not taking up any space on the screen, allowing the parent element to show through.
This discrepancy is likely due to invalid CSS rather than a bug, with each browser doing its best to render the code correctly.
When specifying positioning, consider using either top or bottom, and left or right, along with defining the element's height and width for consistent display across browsers.
If you provide more details on your intended outcome, I would be happy to assist further.
I hope this information proves helpful.