// Called when the user clicks on the browser action
chrome.browserAction.onClicked.addListener(function(tab) {
  // Send a message to the active tab
  chrome.tabs.query({ active: true, currentWindow: true }, function(tabs) {
    var activeTab = tabs[0];
    chrome.tabs.sendMessage(activeTab.id, { message: 'clicked_browser_action' });
  });
});