What exactly does webpack:// mean?

Question

For years I have been building apps with Vue-CLI which bundles Webpack. I see this prefix (protocol?) webpack:// but I don't actually know what it means.

For instance, in the generated source map for an app.xxx.js.map, I see:

{"version":3,"sources":["webpack:///webpack/bootstrap","webpack:///./src/App.vue?797c",...

So what does that webpack:// mean, exactly? It's obviously not a real protocol that the browser can resolve. So resolves it? And how?

The particular problem I'm having that leads me to want to understand this is that my generated chunk-vendors.8c348425.js.map begins like this:

{"version":3,"sources":["webpack:///js/chunk-vendors.68249437.js"],...

In this case, there is no generated chunk-vendors.68249437.js file anywhere. Should there be? Or is that an abstract generated name that doesn't actually refer to a real file?

I'm seeing errors in FireFox that I'm having a bit of trouble interpreting:

I think it's saying that it's (somehow) running that non-existent chunk-vendors.68249437.js file, and that is failing to fetch some (unidentified) resource?