Overview: When a service worker is registered and a user attempts to submit a form that POSTs data to an endpoint that responds with a 307 redirect, the browser does not send the original POST body to the new URI. Steps to Reproduce: 1) Access https://webkit-service-worker-test.herokuapp.com/ 2) Enter any data into the form 3) Submit the form Source code for test: https://github.com/patrickhousley/webkit-service-worker-test Actual Results: In Safari, the page shows no body data was sent when the browser's request was redirected. Attempt the same thing in Chrome or Firefox and the body data will be present. Expected Results: The form data should be sent to the new URI when the browser receives a 307 redirect. Build Date & Hardware: Mac OS X 10.12.6 Safari 11.1.2 (12605.3.8.1)