Also it seems Aquinas supports the idea that the firmament is the atmosphere?
"Another possible explanation is to understand by the firmament that was made on the second day, not that in which the stars are set, but the part of the atmosphere where the clouds are collected, and which has received the name firmament from the firmness and density of the air. "For a body is called firm," that is dense and solid, "thereby differing from a mathematical body" as is remarked by Basil (Hom. iii in Hexaem.)." From (
https://www.newadvent.org/summa/1068.htm#article2)
Also here "If, however, we understand by the firmament that part of the air in which the clouds are collected, then the waters above the firmament must rather be the vapors resolved from the waters which are raised above a part of the atmosphere, and from which the rain falls."
I was also looking at the Haydock commentary on the firmament and it suggested "atmosphere"
I agree it does seem there was a common opinion that the firmament was solid like a wall or something like that but from these quotes and the Haydock commentary it seems it was also an opinion that it wasn't so firm?