CathInfo.com

Like I just pointed out to Aryzia, she holds it to be a necessary article of faith, even though she tried to shroud it in ambiguity. Since there is no Church teaching which defines or even mentions FE, to say someone will not be saved or is not Catholic for not believing in it, is Schismatic.

In the same article you quote above, you will find:  

The Greeks and Stoics adopted a model of celestial spheres after the discovery of the spherical Earthin the 4th to 3rd centuries BCE. The Medieval Scholastics adopted a cosmology that fused the ideas of the Greek philosophers Aristotle and Ptolemy.^[14] This cosmology involved celestial orbs, nested concentrically inside one another, with the earth at the center. The outermost orb contained the stars and the term firmament was then transferred to this orb.

Note the last phrase:  "the term firmament was then transferred to this orb".  The word "firmament" changed its meaning to fit in with the traditional (spherical earth) geocentrism that was the consensus of Catholics for over a thousand years.  The use of the word "firmament" in the 16th century refers to this traditional Catholic sense.  It does not mean that anybody then believed the earth was flat with a dome over it.

While your partial quotes give an impression that the article disagrees with me, it is clear enough when one reads the whole thing that it supports what I have said.

Greeks came up with the spherical earth notion, but ancient peoples before that all held a flat earth world view.  I do not dismiss it lightly when lots of ancient cultures scattered around the world and having little contact with one another happen to come up with a nearly-identical world view.  No, it's not proof of anything, but something to be weighed in the discussion as being of some significance.