function onSet(result) {
  if (result) {
    console.log("success");
  } else {
    console.log("failure");
  }
}

  let getting = browser.privacy.services.passwordSavingEnabled.get({});
  getting.then((got) => {
    console.log(got.value);
    if ((got.levelOfControl === "controlled_by_this_extension") ||
        (got.levelOfControl === "controllable_by_this_extension")) {
      let setting = browser.privacy.services.passwordSavingEnabled.set({
        value: false
      });
      setting.then(onSet);
    } else {
      console.log("Not able to set passwordSavingEnabled");
    }
  });