按下alt时屏蔽点击

firefox用的

// ==UserScript==  
// @name          按下alt时屏蔽点击
// @description   firefox用的
// @version       1
// @match         * 
// @namespace https://greasyfork.org/users/12375
// ==/UserScript==   
  
(function() {  
    let altDown = false;  
    document.addEventListener('keydown', e => e.key === 'Alt' && (altDown = true));  
    document.addEventListener('keyup', e => e.key === 'Alt' && (altDown = false));  
    document.addEventListener('click', e => altDown && (e.preventDefault(), e.stopPropagation()), true);  
})();