STR:
  - Go to https://mozilla.github.io/pdf.js/web/viewer.html
  - Click on "Open File" and open a pdf

The `Download` button and the `Current view` one just disappear.
I can reproduce this bug with Firefox nightly, Chrome stable and Epiphany on debian.
};
    
    loadingTask.onUnsupportedFeature = this.fallback.bind(this);
    return loadingTask.promise.then(
      pdfDocument => {
        this.load(pdfDocument);
      },
      exception => {
        if (loadingTask !== this.pdfLoadingTask) {
          return undefined; 
        }
        let key = "loading_error";
        if (exception instanceof InvalidPDFException) {
          key = "invalid_file_error";
        } else if (exception instanceof MissingPDFException) {
          key = "missing_file_error";
        } else if (exception instanceof UnexpectedResponseException) {
          key = "unexpected_response_error";
        }
        return this.l10n.get(key).then(msg => {
          this._documentError(msg, { message: exception?.message });
          throw exception;
        });
      }
    );
  },
  /**
   * @private
   */
  _ensureDownloadComplete() {