Here is how I tried out: change the service worker to a very simple script, e.g. console.log('hello world'), and see if it works if it works, open safari -> develop menu -> background script window, try to add the actual service worker script into the background console using copy and paste, and see if there is any error however, in my case, I actually forgot to add the 'service-worker.js' into the web extension project (i.e. add file reference to the xcode project), since it's a new file created solely for the migration purpose, and it only contains one line of 'importScripts(...)'.