Browser Extension code to intercept top-level navigations directly to audio/video files and instead navigate to a playback page that allows the user to play the response inside the browser itself.

InterceptTopLevelNavigations.js

// Note, you need to update the "permissions" section of your manifest.json
// to contain ["webRequest", "webRequestBlocking"]

// Watch for top-frame navigations directly to media files. If found, instead navigate to a player page.
browser.webRequest.onHeadersReceived.addListener(
  function(details) {
  	// We don't care about redirects or error responses.
  	if (details.statusCode !== 200) return;
  	
  	// Skip navigations that aren't to Audio/Video
  	let sCT = extractContentType(details.responseHeaders).toLowerCase(); 	
  	if (!(sCT.startsWith("audio/") || sCT.startsWith("video/") || (sCT.startsWith("application/ogg")))) return;
  	
  	// Redirect to a player page.
  	return {
  		redirectUrl: ("https://bayden.com/test/play.aspx?ct=" + encodeURIComponent(sCT) + "&u=" + encodeURIComponent(details.url))
  	};
  },
  {urls:["<all_urls>"], types:["main_frame"] },
  ["blocking","responseHeaders"]
);