According to the context of our verse the open firmament is where birds fly, so it's the atmosphere or sky. We can consider it to be the first of three heavens.
Firmament 3
Firmament 2
And God said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years:
The Firmament Rabbit Trail
One of our favorite ways to study the Bible is to follow a doctrine through from the first time it's mentioned to the last. This is a great way to develop understanding of the doctrine in the broad narrative of scripture.
April 23rd
There's no need to speculate the existence of black holes or dark matter. The missing mass of the universe is the firmament.
Transit of Venus
Any time that someone uses the transit of Venus as proof of heliocentricity they’re demonstrating that their knowledge of the subject matter is at or below a superficial level.
December 4th
Life is temporary. What comes next? God's given us a description of what comes next and the choice of whether or not to believe it. We acknowledge belief in God's testimony by accepting Jesus Christ as our savior.
December 1st
We refer to the life after this one as "heaven" because we haven't paid attention to what the Bible says. We'll eventually live in a new Jerusalem at the the location presently occupied by our Earth.
November 19th
The expansion of hell will cause the conditions on the earth to become worse than we have imagined possible. Hell is not going away until after the Millennial Kingdom, therefore we have to be insulated from it.
Retrograde Motion
Retrograde motion is often described as a "big problem" for the Geocentrospheric model, but this exposes a failure by those who believe this to comprehend two concepts frame of reference and relative motion.
Moons of Jupiter
Any time someone uses the moons of Jupiter as proof of heliocentricity they're demonstrating that their knowledge of the subject matter is at or below a superficial level.