// Allows users to open the side panel by clicking on the action toolbar icon
chrome.sidePanel
  .setPanelBehavior({ openPanelOnActionClick: true })
  .catch((error) => console.error(error));

chrome.action.onClicked.addListener(() => {
  chrome.tabs.create({
    url: 'mainpage.html'
  });
  console.log('Opened a tab with a sandboxed page!');
});