This is really interesting. I have an idea where this could be helpful to the Plex user community. Recently Plex added a header that blocks the page from being iframed (X-Frame-Options).

Would doing something like this, obviously replacing example.com with their own domain.com, replace the offending header?

  addEventListener('fetch', event => {  
    let request = event.request;
    if (request.headers.has('X-Frame-Options')) {
      let newHeaders = new Headers(request.headers);
      newHeaders.set('X-Frame-Options', 'ALLOW-FROM https://example.com/');
      event.respondWith(fetch(request, {headers: newHeaders}));
    }
  
    // Use default behavior.
    return;
  });