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.
if (this.pdfViewer.isInPresentationMode) {
      return;
    }
    this.pdfViewer.currentScaleValue = DEFAULT_SCALE_VALUE;
  },
  get pagesCount() {
    return this.pdfDocument ? this.pdfDocument.numPages : 0;
  },
  get page() {
    return this.pdfViewer.currentPageNumber;
  },
  set page(val) {
    this.pdfViewer.currentPageNumber = val;
  },
  get supportsPrinting() {
    return PDFPrintServiceFactory.instance.supportsPrinting;
  },
  get supportsFullscreen() {
    if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("MOZCENTRAL")) {
      return shadow(this, "supportsFullscreen", document.fullscreenEnabled);
    }
    return shadow(
      this,
      "supportsFullscreen",
      document.fullscreenEnabled ||
        document.mozFullScreenEnabled ||
        document.webkitFullscreenEnabled
    );
  },
  get supportsIntegratedFind() {