We will come to the word firmament again, but notice that this is, "... the likeness of the firmament ...", not the firmament itself. Later verses speak only of the "firmament".

23. And under the firmaments were their wings straight, the one toward the other: every one had two, which covered on this side, and every one had two which covered on that side, their bodies.

If you changed "... under the firmament ..." to, "... below the sky" you would get a clearer picture. If you look at the picture of a house, the roof is, "below the sky," if you start at the top and work down. If you start at the ground and work up, the roof is, "at the top" of the house. Ezekiel's description of the wings, which is continued in this verse, concerns the wings "at the top." They are (connected), "... one toward the other, about like in figure one."

24. And when they went, I heard the noise of their wings, like the noise of great waters, like the voice of the Almighty, the voice of speech, as the noise of the host: when they stood they let down their wings.

If you have ever stood near a running tip-jet, or any jet engine, I think you will know what Ezekiel means. The last statement is most interesting. It seems that when the creatures landed again they detached the helicopter mechanisms and set them down, as anyone will with a heavy back-pack who is resting or waiting.

25. And there was a voice from the firmament that was over their heads, when they stood, and had let down their wings.

This voice, or sound, was not from the likeness of the firmament, but from the sky, as they stood there with their wings off.

This is the end of Ezekiel's attention to the four creatures.

26. And above the firmament that was over their heads was the likeness of a throne, as the appearance of a sapphire stone; and upon the likeness of the throne was the likeness as the appearance of a man above upon it.

Out of the sky comes a man on a green seat. But a throne is more than a chair. It is usually associated with a platform. This may be some kind of flying platform similar to those being tested for the transporting of infantry.