I got things completely wrong. The issue was that the wapm.wasm program was doing an HTTP request with a custom "User-Agent", and Firefox was blocking it becaus

I got things completely wrong. The issue was that the wapm.wasm program was doing an HTTP request with a custom "User-Agent", and Firefox was blocking it because of that but showing the wrong message in the console. Good news is... right now things work as they should in Firefox!