I've already tried different ways to construct the blob and the base64 binary, but none of them worked.

getThumbnail.js

dropbox.getThumbnail(file.path_lower, 'jpeg', 'w64h64').
  then((response) => {
    console.log(response)
    //let thumbnailBlob = window.btoa(unescape(encodeURIComponent(response.text)));
    //file.thumbnailLink = 'data:image/jpeg;base64,' + thumbnailBlob;
    let arrayBufferView = new Uint32Array(response.text);
    let thumbnailBlob = new Blob([arrayBufferView], {type: "image/jpeg"});
    file.thumbnailLink = window.URL.createObjectURL(thumbnailBlob);
    console.log(thumbnailBlob);
    console.log(file.thumbnailLink)
  }, (err) => reject(err));