I wrote a glitch to echo our FetchEvent attributes: https://fetch-event-echo.glitch.me/ I noticed while using this that we set a pretty bogus accept header for worker scripts: accept,text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 It seems completely wrong to be advertising text/html here.

Note, if you want to try the glitch, you need to manually load a worker through the web console: var w = new Worker('worker-location.js');

Per step 1.3 here we should be setting "*/*" for worker scripts: https://fetch.spec.whatwg.org/#fetching