'Firmament' stems from the Latin word 'firmamentum' and is derived from 'firmus', solid. This confirms your concordance, so I don't know where you got the idea from that the bible's sky is not solid. Also last time I checked, birds had no problems to fly in vaults, although bats are more likely to do that.

And what about the other objections - where is the water above the firmament, and why do you assume that God created only half an atmosphere?

- You're certainly right that the bible is no scientific manual. This is just the reason for the difficulties you're already getting in the attempt to bend that single sentence so that it can be taken literally. And there are many, many more such sentences in Genesis and the rest of the bible that you'd have to distort even worse. How about "He separated the light from the darkness and called the light day and the darkness night"? How would you literally explain that?