[kevincox]

I don't think this will work well as a third party. Since service workers are so powerful they are quite tricky to get set up. You would need to serve it from the domain of the page that you want to intercept. You are probably much better off using a user-script or browser extension for this. I think both provide APIs for request interception but for your use case it may be easier to wrap and intercept the `fetch` or `XMLHttpRequest` API.