A little script for refreshing all gifs on a webpage to make them synchronized.

syncgif.js

(function refreshGif(selector, images, srcs) {
  var mode = !!srcs, i;
  if(mode) {
    for(i = 0; i < images.length; i++)
      images[i].src = srcs[i];
    return;
  }
  var dummyGif = 'data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==';
  images = document.querySelectorAll((selector || '') + ' img[src$=\'.gif\']');
  srcs = [];
  for(i = 0; i < images.length; i++) {
    srcs[i] = images[i].src;
    images[i].src = dummyGif;
  }
  setTimeout(refreshGif, 0, selector, images, srcs);
})();

/* Alternative you may copy this bookmarklet:
   javascript:(function()%7B!function%20A(e%2Cr%2Cl)%7Bvar%20t%3Bif(!!l)for(t%3D0%3Bt%3Cr.length%3Bt%2B%2B)r%5Bt%5D.src%3Dl%5Bt%5D%3Belse%7Bfor(r%3Ddocument.querySelectorAll((e%7C%7C%22%22)%2B%22%20img%5Bsrc%24%3D'.gif'%5D%22)%2Cl%3D%5B%5D%2Ct%3D0%3Bt%3Cr.length%3Bt%2B%2B)l%5Bt%5D%3Dr%5Bt%5D.src%2Cr%5Bt%5D.src%3D%22data%3Aimage%2Fgif%3Bbase64%2CR0lGODlhAQABAIAAAP%2F%2F%2FwAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw%3D%3D%22%3BsetTimeout(A%2C0%2Ce%2Cr%2Cl)%7D%7D()%7D)()
*/