background.js

var notification, reverse, mouse_button, key, links_status, open_grabbing_cursor, close_grabbing_cursor;
var grabbing = true;
var css = 'a {pointer-events: none;};';
var browser_action_on_icons = {16: "icons/grabbing-16.png", 32: "icons/grabbing-32.png"};
var browser_action_off_icons = {16: "icons/grabbing-off-16.png", 32: "icons/grabbing-off-32.png"};

function log(msg){
  console.log(msg);
}

function onError(error) {
  console.error(`Error: ${error}`);
}

function restoreOptions() {
  function setCurrentChoice(result) {
    notification = (result.notification == undefined)? false : result.notification;
    reverse = (result.reverse == undefined)? false : result.reverse;
    mouse_button = (result.mouse_button == undefined)? "Left" : result.mouse_button[0];
    key = (result.key == undefined)? "<Ctrl>|<Alt>|<Shift>" : result.key[0];
    links_status = (result.links == undefined)? "Non-clickable" : result.links[0];
    open_grabbing_cursor = (result.open_grabbing_cursor == undefined)? "" : result.open_grabbing_cursor;
    close_grabbing_cursor = (result.close_grabbing_cursor == undefined)? "" : result.close_grabbing_cursor;
  }

  var getting = browser.storage.local.get(["notification", "reverse", "mouse_button", "key", "links", 
    "open_grabbing_cursor", "close_grabbing_cursor"]);
  getting.then(setCurrentChoice, onError);
}

restoreOptions();

function toggle_grabbing() {
  if (grabbing == true) {
    grabbing = false;
  } else {
    grabbing = true;
    restoreOptions();
  }
  browser.browserAction.setIcon({path: grabbing ? browser_action_on_icons : browser_action_off_icons});
  sendMessageToTabs();
}

function sendMessageToTabsCallbak(tabs) {
  for (let tab of tabs) {
    if (grabbing && (links_status == 'Non-clickable')) {
      browser.tabs.insertCSS({code: css}) 
    } else {
      browser.tabs.removeCSS({code: css})
    }
    var opt = {
      notification: notification,
      reverse: reverse,
      mouse_button: mouse_button,
      key: key,
      links_status: links_status,
      open_grabbing_cursor: open_grabbing_cursor,
      close_grabbing_cursor: close_grabbing_cursor
    }
    browser.tabs.sendMessage(tab.id, {grabbing: grabbing, options: opt}).then(response => {}).catch(onError);
  }
}

function sendMessageToTabs() {
  browser.tabs.query({
    active: true
  }).then(sendMessageToTabsCallbak).catch(onError);
}

function handleActivated(activeInfo) {
  if (grabbing) browser.tabs.insertCSS({code: css});
  sendMessageToTabs();
}

function handleUpdated(tabId, changeInfo, tabInfo) {
  if (changeInfo.status == "complete"){ sendMessageToTabs() };
}

browser.tabs.onUpdated.addListener(handleUpdated);
browser.tabs.onActivated.addListener(handleActivated);
browser.browserAction.onClicked.addListener(toggle_grabbing);

function handleMessage(request, sender, sendResponse) {
  if (request.grabbing == true || request.grabbing == false) toggle_grabbing()
}

browser.runtime.onMessage.addListener(handleMessage);