In Safari, no-op mode doesn't work as the line below returns true. https://github.com/mozilla/webextension-polyfill/blob/f818ecbac3c0a4b67998014a16898210cf80e715/src/browser-polyfill.js#L13 Strangely, the browser object on Safari inherits `CallbackObject`. So `Object.getPrototypeOf(globalThis.browser)` doesn't return `Object`. `Object.getPrototypeOf(Object.getPrototypeOf(globalThis.browser)) !== Object.prototype` finally gives the expected value. 
In Safari, no-op mode doesn't work as the line below returns true.
webextension-polyfill/src/browser-polyfill.js
Line 13 in f818ecb
Strangely, the browser object on Safari inherits
CallbackObject. SoObject.getPrototypeOf(globalThis.browser)doesn't returnObject.Object.getPrototypeOf(Object.getPrototypeOf(globalThis.browser)) !== Object.prototypefinally gives the expected value.