Sadly a lot of browser features are inaccessible from non-https contexts.

Don't most (all?) browsers consider file:// and localhost to be secure for the sake of enabling those features?

https://developer.mozilla.org/en-US/docs/Web/Security/Defens...

Unfortunately, no. CORS will block this on Chrome and Firefox.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Guides/COR...

The security risk : https://www.mozilla.org/en-US/security/advisories/mfsa2019-2...

You need a local webserver. Or bundle everything in one html file.

or you could use something like caddy (https reverse-proxy, local cert), and have a dedicated ws running in the background that serves your files