Page doesn't load. A ServiceWorker passed a promise to FetchEvent.respondWith() that rejected with ‘TypeError: NetworkError when attempting to fetch resource

[kovan]

After some testing with this template, I have gotten to a point where Firefox doesn't show anything, it says:

The site at http://localhost:3000/ has experienced a network protocol violation that cannot be repaired.

Reloading the page or restarting the server don't fix it, the browser gets kind of stuck in that situation.

The only way to fix it is deleting the service worker from the browser, but after a while it reappears.

In the Firefox console, I get two errors:

Failed to load ‘http://localhost:3000/’. A ServiceWorker passed a promise to FetchEvent.respondWith() that rejected with ‘TypeError: NetworkError when attempting to fetch resource.’.
No strings exist for error: corruptedContentErrorv2-title

I have run the app with "npm run dev`.