Prevent modifying `browser` after patching?

[4ntoine]

We're going to use it with Safari that is not supported at the moment.
I try to patch it as follows:

import browser from "webextension-polyfill"

let historyApiPrototype = {
  __listeners: new Map(),
  addListener(listener, filter) {
    if (this.hasListener(listener)) {
      return;
    }
    this.__listeners.set(listener, filter);
  },
  removeListener(listener) {
    this.__listeners.delete(listener);
  },
  hasListener(listener) {
    return this.__listeners.has(listener);
  }
};

if (!browser.webNavigation.onHistoryStateUpdated) {
      browser.webNavigation.onHistoryStateUpdated =
    Object.create(historyApiPrototype);
    }

However after some time i can see the browser object is recovered back and browser.webNavigation.onHistoryStateUpdated is undefined.
Is it expected? How can i prevent recovering? Will it help if i patch chrome object earlier than webextension-polyfill is imported for the first time?

[Rob--W]

The browser object returned in Safari is the native, built-in browser object. Do you see this behavior even without the polyfill?