setPreviewThumbnails(thumbnailSource) {
    if (this.previewThumbnails && this.previewThumbnails.loaded) {
      this.previewThumbnails.destroy();
      this.previewThumbnails = null;
    }

    Object.assign(this.config.previewThumbnails, thumbnailSource);

    // Create new instance if it is still enabled
    if (this.config.previewThumbnails.enabled) {
      this.previewThumbnails = new PreviewThumbnails(this);
    }
  }
Sets the preview thumbnails for the current source