For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
Would the idea of the firmament be any different than what we know now?
I know that some people see this as a liquid water or ice barrier that existed at one time in the atmosphere as the firmament. I can see no specific Biblical reference to support this idea.
I think it is more likely that this refers to water vapor like clouds just as we know it today. Some people say it was more dense.
It's interesting that the flood narrative refers to both the "fountains of the deep" and the "windows of the heavens", going on to say that when the rain was finished they were both closed. This seems to me to indicate the same structure remained in place and that it didn't "collapse" during the flood as I've seen some say.
Windows of the heavens are also referenced in Malachi 3:10 and Psalm 78:23 as the source of blessing and provision. It brings up an interesting point, in that God's punishment on humanity came by the same path as his blessing. I think this speaks to his nature. That He is always good.