Of course, the reference to a solid firmament is a huge signal that reminds us of the need to read the creation narratives in their ancient Near Eastern context, rather than try to read them through 21st century eyes, using modern concepts of historiography. (Ironically, the same mistake is made by atheists who also read the creation narratives through the same historiographical lens, and reject the creation narratives for the same reason. Fundamentalists are fundamentalists, irrespective of whether they are atheist or theistic).
Another key to reading the narratives is to reognise the concept of divine accommodation. Christadelphians should not find this hard to grasp as we've used this hermeneutical strategy when reading the accounts of demon possession in the NT. We know that disease is not caused by a head filled with demons, but in the parts of 1st century Israel where this belief was endemic, Jesus accommodated this view, rather than waste time trying to disabuse them of this belief. The same approach pays dividends in Genesis 1, and it is one which is actually quite old, dating back to John Calvin. In his commentary on Genesis, he notes that it defied common sense to believe that there were 'waters above the heaven', and then opined that this was an example of how the narrative accommodated human finitude:
Moses describes the special use of this expanse, “to divide the waters from the waters,” from which words arises a great difficulty. For it appears opposed to common sense, and quite incredible, that there should be waters above the heaven. Hence some resort to allegory, and philosophize concerning angels; but quite beside the purpose. For, to my mind, this is a certain principle, that nothing is here treated of but the visible form of the world. He who would learn astronomy, and other recondite arts, let him go elsewhere. Here the Spirit of God would teach all men without exception; and therefore what Gregory declares falsely and in vain respecting statues and pictures is truly applicable to the history of the creation, namely, that it is the book of the unlearned. The things, therefore, which he relates, serve as the garniture of that theatre which he places before our eyes. Whence I conclude, that the waters here meant are such as the rude and unlearned may perceive. [3]
There's an old saying which says it's better to be imprecise and understandable, rather than strive for accuracy but never be understood. Accommodating ANE views on the world in order to teach a theological point makes perfect sense when you think about the sheer difficulty of trying to teach a Copernican cosmology to an Iron Age audience. The trick for modern exegetes is to read the text with ancient eyes and modern questions.
References
1. Schadewald R "Scientific Creationism, Geocentricity, and the Flat Earth" Skeptical Inquirer, Winter 1981-1982
2. Enns P "The Firmament of Genesis 1 is Solid but That's Not the Point" Science and the Sacred January 14 2010
3. John Calvin and John King, Commentary on the First Book of Moses Called Genesis (Bellingham, WA: Logos Bible Software, 2010), 79–80.