Here's a screenshot from my console
Anyway, the solution, after some trial and error, was to instead of using async-local-storage.min.js I have to use async-local-storage-with-Promise.min.js and then it works.
It was my mistake for downloading the wrong .min.js file ultimately but I typed "Promise" on the console and it already existed. Apparently this is a built-in Promise function in Firefox that clearly works slightly differently.
Here's what the built-n Promise thing looks like in Firefox
Perhaps the right thing to do is to do something like:
if (!Promise.isThenable) { throw "Promise library not loaded" }