Mikey, my humble and most sincere apologies! It was indeed my mac.
I fixed it and was able to serve pages from my mac via Emporter to a browser outside my own network.
You probably want to know what it was? Ahum it was ‘over zealous anti-malware software’
Kaspersky to be exact (not the first time it messed things up, but certainly the last: gone, bye Kaspersky!).
Although I had it turned off, there was still something running. Removing it completely solved the problem.
So… I concur with @teefers and @peterdanckwerts Emporter does work on Mojave.
And also on… Catalina!