bilibili-cover.user.js

// ==UserScript==
// @name        Bilibili Cover
// @namespace   http://t.qq.com/HeartBlade
// @description 显示视频封面
// @include     http://www.bilibili.com/video/av*
// @include     https://www.bilibili.com/video/av*
// @version     1.3
// @grant       GM_addStyle
// ==/UserScript==
var cover_box=document.createElement("div");
cover_box.id="cover_box";
var cover_image=getCoverImage();
    
cover_image.id="cover_image";
var cover_text=document.createElement("span");
cover_text.textContent="视频封面";
cover_text.id="cover_text";
cover_box.appendChild(cover_text);
cover_box.appendChild(cover_image);
getLiveBox().then(liveBox => liveBox.parentNode.insertBefore(cover_box, liveBox));
var css=`
  .elecrank-wrapper{
    padding:30px 0px 0px 10px;
  }
  #cover_box{
    padding-left:10px;
    padding-top:38px;
  }
  #cover_box img{
    display:inline!important;
    width:258px;
    height:auto;
    margin-top:20px;
  }
  #cover_text{font-size:16px}
  .r-wrapper > #cover_box {
    padding-bottom: 38px;
  }
`;
GM_addStyle(css);

function getLiveBox() {
  return new Promise(resolve => {
    (function recursive() {
      const liveBox = document.querySelector(".v-live-recommend, .pop-live");
      if (liveBox) {
        resolve(liveBox);
      } else {
        setTimeout(recursive, 200);
      }
    })();
  });
}

function getCoverImage() {
  const url = getUrl();
  const a = document.createElement("a");
  const img = new Image;
  a.title = "Bilibili Cover";
  a.href = url;
  a.target = "_blank";
  img.src = url;
  a.appendChild(img);
  return a;
  
  function getUrl() {
    const coverImage = document.querySelector(".cover_image");
    if (coverImage) {
      return coverImage.src;
    }
    return unsafeWindow.__INITIAL_STATE__.videoData.pic;
  }
}

https://greasyfork.org/en/forum/discussion/34077/