It is very possible that Firefly wrote a lot of utility themselves, but we should always consider that some of the standard functions might inline or be intrinsics. Typical cases for this might be some (not all) cstring and memory functions.
A good source for the intrinsics is intrin.h, but I do not know, if this files contains all.
Additionall, some header code contains inline code, so there might also be cases where stuff is inlined.
This issue is meant as a collection. If structures are identified, feel free to put them here (assuming Ghidra is unable to identifiy them).