var req = new XMLHttpRequest();
req.open('GET', 'https://discord.com/api/v6/users/@me', false);
req.setRequestHeader('Authorization', 'Bearer ' + window.location.href.match(/access_token=([\w\d-]+)/)[1]);
req.send(null);
console.log(req.responseText);

// Simply open your browser's console (usually by pressing F12), paste in the code, and hit enter. The console should print out your Discord user information, including your token.