Is the firmament a solid dome?

No, the firmament is not a solid dome. The firmament was a spherical structure that God built to hold back the water from the earth, and then it was stretched out into the remote recesses of space and became ethereal. That is why the stars, planets, and sun could be placed in it, as Genesis 1:14 says, because by then it was ethereal, not solid. It was solid at one time, a spherical structure that could hold up the water on the second day, but once it was stretched out it carried everything with it and became the second heaven, where God set the stars on the fourth day. The first heaven is where the birds fly, the second heaven is where the stars are, and the third heaven is where God and the angels are. So it is not a solid dome; it is not solid in the sense that you cannot put your hand through it. It used to be solid, and now it is ethereal.