Misskeyも/shareがあるってことは、TamperMonkeyとかGreaseMonkeyにこれ突っ込んだら、Web上のツイートボタンが全部Misskeyにリダイレクトされる…ってコト！？

// ==UserScript==
// @name        birds gone somewhere
// @match     https://twitter.com/intent/tweet*
// @version     0.1
// @description  override tweet button to the toot to mastodon.

// ==/UserScript==

var base = "https://misskey.io/share?text=";
var url = location.href.split('?')[1].split('&');
var twtext = "";
var twurl = "";
for (var i = 0; i < url.length; i++) {
  var j = url[i].split('=');
  if (j[0] == 'text') {
    twtext = j[1];
  }
  if (j[0] == 'url') {
    twurl = "%0D%0A" + j[1];
  }
}
var newurl = base + twtext;
if (twurl) { newurl += twurl; }
location.href = newurl;