Firefox Service Worker import module giving TypeError

SW Registration failed with TypeError: ServiceWorker script at http://localhost/Vanilla/CacheManager.js for scope http://localhost/Vanilla/ threw an exception during script evaluation.

I’m getting the above TypeError when trying to register a ServiceWorker with FireFox (Works on Chrome, Wsdge, Opera) –

if ("serviceWorker" in navigator) {                 
    await navigator.serviceWorker.register('/Vanilla/CacheManager.js', { scope: '/Vanilla/', type: 'module' })
        .then(reg => {
                console.log('SW Registered');
            })
        .catch(err => {
            console.log('SW Registration failed with ' + err)
        });

CacheManager.js (reduced to) –

*import config from "/Vanilla/config.js"* **// The problem**
console.log("Hello")
//const CACHE_NAME = config.cacheName   

Config.js

export const config = 
{
    "cacheName": "VanillaV1.1"
}

I have no idea what TypeError FireFox is complaining about. CONST?