I just tried it again, and it worked! This is what I did:
I clicked on “Install-AdNauseam-on-Chrome-Without-Google’s-Permission”, which told me it had moved to https://github.com/dhowe/AdNauseam/wiki/Install-AdNauseam-on-Chromium-based-browsers
I followed the intructions given under https://github.com/dhowe/AdNauseam/wiki/Install-AdNauseam-on-Chromium-based-browsers#install-adnauseam
Goodness knows what I was doing wrong last March!