The Bible wasn't written in English, Void.
The word 'firmament' itself first entered the English lexicon around the 13th century, stemming from the Latin 'firmenmentum', which means 'strengthening' or 'expanse'.
The Hebrew word used here is 'raqia', which means 'expanse'.
No mention of plexiglass, Void.
Plexiglass is a colloquial (marketing name) for lucite plastic panels. The stuff was invented by DuPont in 1935. It is used to produce shatterproof glass windows (safety glass), as well as a lightweight material for luminare coverings.
There is no plexiglass sphere in the sky. I have heard of this religion before that believes there is. Apparently you are a believer in this religion also. You are the 2nd one I have found with this religion.
Too bad you depend on constellations of satellites and benefit from spacecraft sent to the Moon.