The firmament in Genesis 1:6-8 is the cloud that thee LORD covered the earth with like a garment.
A cloud body of gaseous matter. Atmosphere.
4 Where wast thou when I laid the foundations of the earth? declare, if thou hast understanding.
5 Who hath laid the measures thereof, if thou knowest? or who hath stretched the line upon it?
6 Whereupon are the foundations thereof fastened? or who laid the corner stone thereof;
Job 38:4-6
When I made the cloud the garment thereof, and thick darkness a swaddlingband for it, Job 38:9
So what light did your God see when he saw the light?
3 And God said, Let there be light: and there was light. 4 And God saw the light, that it was good: and God divided the light from the darkness.
Gen 1:3-4
Genesis 1:6-8 6And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters. 7And God made the firmament, and divided the waters which were( under the firmament from the waters which were above the firmament): and it was so. 8And God called the firmament Heaven. And the evening and the morning were the second day
You said- A cloud body of gaseous matter. Atmosphere. That's not a the firmament