Ah, webfonts, our friends when they work and our nightmare when they don’t. Right now (May 2020) I am running the blog using iA Writer Duo, it feels like a monospace but it is not. It is based on IBM Plex, that on turn was based on Nitti, all by Bold Monday. In the Duo version the proportions of M and W are a little bit more roman and a little bit less monospace. They explained it very well in this post.
If you are seeing this in Firefox Chances are you will read it in Duo, but in Chrome and Safari if the webfonts are not uploaded, you will get, well, a sanserif, probably Helvetica. The idea of Courier seems revolting so the code goes font-family: "iA Writer Duospace", sans-serif;. Suggestions to make it better are more than welcome.