function saveOptions(e) {
  browser.storage.sync.set({
    commentsRemove: document.getElementById("commentsRemoveCheck").checked
  });
  e.preventDefault();
}

function restoreOptions() {
  var gettingItem = browser.storage.sync.get({commentsRemove: false});
  gettingItem.then((res) => {
    document.getElementById("commentsRemoveCheck").checked = res.commentsRemove;
  });
}

document.addEventListener('DOMContentLoaded', restoreOptions);
document.querySelector("form").addEventListener("submit", saveOptions);