If Jr Knowing's argument is that von Braun simply meant to refer to the archaic notion of the firmament as an actual solid dome, then he doesn't need to maintain a belief in it or even argue that von Braun believed it. It would be like me referring to Cerberus; the mythical connotation may be all I need to make my point without outright expressing an actual belief in a giant three-headed dog. We all know what the reference means. The difference, of course, is that Cerberus -- even as a myth -- is a pretty locked-down concept. What "firmament" means to people who read the Bible has changed quite a bit over the years from its archaic meaning, and has even lately acquired a number of poetic or symbolic meanings. To affirm, with no evidence whatsoever, that a certain person (now beyond our reach) must have intended only one of these meanings is irrational.
And if you want to perpetuate a debate forever without any sort of resolution, that sort of circumstance is ideal. Jr Knowing is now in the hogs-heaven (or hogs-firmament) of conspiracy claimants. Regardless of the actual title of this thread, he's successfully changed its subject to one that can be debated ad nauseam without any hope of a factually-supported resolution. The only way to resolve this conclusively would be to peek into the mind of a man who's been dead for more than forty years in the hope of determining (or refuting) what he was thinking at the time he chose the verse. The "debate" now is just endless second-guessing, assumption, and supposition on both sides. He has thoroughly rebuffed any attempt to bring the debate back to questions that can actually be resolved, or even questions that bear the slightest resemblance to the original topic.
If you want evidence that he's not interested in a serious debate, there it is.