Firefox triggers Websocket error from IAsyncEnumerable Core MVC controller method

I am using a cancellable Javascript Fetch to retrieve a C# Microsoft.AspNet.WebApi.Core IAsyncEnumerable Controller method. There is no error with Chrome or Edge but Firefox logs the following: -

I don't know if it is a W3C standard to convert a HTTP Fetch into a Websocket for Streaming or how Microsoft manages to embed it's Browser-Link virus

This is plain .html not .cshtml or Razor pages.

Can anyone shed light on what's happening?

Here's the JS code: -

	<script type="application/javascript">

	async function doit()
	{
		  const decoder = new TextDecoder();

		  const abortControl = new AbortController();
		  const signal = abortControl.signal;
		  setTimeout(() =>
			{
				abortControl.abort();
				console.log("*ABORTED*")
			}, 2000); // Simulate a cancel after 2 secs

		  const fetchOpts = {signal:signal, method:'GET', cache:"no-cache"};
		  const response = await fetch("https://localhost:7196/data/yieldfamilyname?inname=made", fetchOpts);
		  const reader = response.body.getReader();

		  let result = await reader.read();

		  while (!result.done && !signal.aborted)
		  {
				var personText = decoder.decode(result.value).replace(/\[|]/g, '').replace(/^,/, '');
				var person = JSON.parse(personText);
				console.log("chunk is", person.familyName);

				try {
					result = await reader.read();
				}
				catch (err) {
					console.log(err.message);
					break;
				}
		  }
		  reader.releaseLock();
	}

	doit()
</script>

After the first Yield these messages are logged: -

chunk is MADE fred.html:32:14

Use of Mutation Events is deprecated. Use MutationObserver instead. browserLink:3299:5701

Tools extension connected browserLink:50:1248

Initializing tools services... browserLink:50:1248

Initializing tools design surface service browserLink:50:1248

Initializing tools selection service browserLink:50:1248

Initializing tools tag navigation service browserLink:50:1248

Initializing tools hotkey manager service browserLink:50:1248

Host extension connected browserLink:50:1248

Initializing host services... browserLink:50:1248

chunk is MADEBGWE fred.html:32:14

Firefox can’t establish a connection to the server at wss://localhost:44312/ChunkIt/.
aspnetcore-browser-refresh.js:234:24

WebSocket failed to connect. aspnetcore-browser-refresh.js:18:15

chunk is . . . .

ABORTED fred.html:19:14

The operation was aborted. fred.html:38:15

I found the answer here

It appears the insidious script injection is so omni-present and all pervasive that .NET searches all served up content looking for an end-body tag. My old code that used document.write to report an error had one line converted to: -

topWindow.write('<p style="color:red">' + message + "</p><script src="/_framework/aspnetcore-browser-refresh.js"></script></body></html>");

If it wasn't syntactically invalid, I probably wouldn't have known