what next? stop calling people humans and call them hupersons instead?
As far as I know (and rather surprisingly), there is no known connection between the words "man" and "human". "man" is Germanic, going back a long way because it's common to various different Germanic languages (and must therefore predate the splits). "human" traces back to Latin, i.e. not Germanic at all. A connection seems obvious, but as far as I know there isn't a known one. A suspected one back to Proto Indo-European, perhaps, but nothing is known about that language. There's good reason to think it existed, but we're going back long before recorded history and it's all speculation.
Pretty sure the "man" part in fireman, policeman, etc comes from the "man" in human. Like many words in English, man has more than one meaning.
The "man" part in fireman, policeman, etc, comes from the word "man" (meaning "person") in Germanic languages. Old English in this case, obviously, but it's also found in other Germanic languages. (EDIT for clarity: I specified Old English because that was definitely a Germanic language and it's the origin of the word "man" in middle and modern English, so even when the compound words are middle or modern English the "man" part comes from Old English).
It's only in the last few decades that the meaning of the word "man" has been changed in English to be male-specific. For millenia, it meant "person". All of the compound words using the word "man" predate that change. Even the ones that no longer include it, such as midwifman ("mid" + "wif" + "man" = "with/helping female person", now shortened to "midwife").
That's why if you look back even just a little way you will find things such as a medical paper entitled "The uterus in rats and men". That made perfect sense until very recently because "men" meant "people". Another example off the top of my head is English translations of the Magna Carta. Unless you're looking at a very recent and carefully done retranslation into
very modern English, it will be using the word "men". For example, here is the translation from the library of the British Library.
https://www.bl.uk/magna-carta/articles/magna-carta-english-translation
Note, for example, the initial statement regarding who the charter applies to:
TO ALL FREE MEN OF OUR KINGDOM we have also granted, for us and our heirs for ever, all the liberties written out below, to have and to keep for them and their heirs, of us and our heirs:
The
original text for that section, i.e. stating what the authors of the charter meant:
Concessimus eciam omnibus liberis hominibus regni nostri, pro nobis et heredibus nostri in perpetuum, omnes libertates subscriptas, habendas et tenendas eis et heredibus suis, de nobis et heredibus nostris.
Note that the word translated as "men" is "hominibus", which is sex-neutral. If the authors had intended it to apply to male adults only, they would have written "viri", not "hominibus". The distinction is very clear in Latin. It's not a mistranslation - the translator used "men" as the English word for "people" because that was entirely correct until very recently, so the translation was correct when it was done.