Funnily enough (not funny actually, considering the war crimes and all), the Old Testament says that the Jews/Isrealites will never get rid of other people living in the area due to not driving them out in their original conquest.

Interesting, I've not heard of this shell of ice, and I believe in a young earth. I have heard though of a similar hypothesis based in Genesis 2:5-6 which proposes that it did not rain before Noah's flood and that plants were kept watered by a heavy mist and/or extremely humid atmosphere. Acoording to this idea, that excess water in the air and ground would've been all condensed by God as part of the flood.

I'm not sure I entirely agree with the hypothesis, and I do not believe it is essential biblical knowledge so I don't concern myself with it, but I have heard it before.

I agree with others, this seems like a flat-earther belief that has gotten mixed with Christianity's creation story.

I've heard of it before while browsing the internet, but not from any Christians I personally know. All the Christians I interact with (myself included) believe in a literal interpretation of the creation but nobe of us believe in a physical firmament. I will note that a single man I know denies the moon landing (for reasons I haven't bothered to ask) but even he still believes in a spherical earth and heliocentric orbit.

My understanding of Genesis 1:6-8 is that the firmament mentioned is the earth's sky or atmosphere itself, and not a physical barrier at the edge of the atmosphere. The easiest way to show this would be Genesis 1:20 where birds are described as "flying in the firmament of heaven". If the firmament was a solid object, birds could not fly in it.