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.
linkService: pdfLinkService,
    });
    this.pdfAttachmentViewer = new PDFAttachmentViewer({
      container: appConfig.sidebar.attachmentsView,
      eventBus,
      downloadManager,
    });
    this.pdfLayerViewer = new PDFLayerViewer({
      container: appConfig.sidebar.layersView,
      eventBus,
      l10n: this.l10n,
    });
    this.pdfSidebar = new PDFSidebar({
      elements: appConfig.sidebar,
      pdfViewer: this.pdfViewer,
      pdfThumbnailViewer: this.pdfThumbnailViewer,
      eventBus,
      l10n: this.l10n,
    });
    this.pdfSidebar.onToggled = this.forceRendering.bind(this);
    this.pdfSidebarResizer = new PDFSidebarResizer(
      appConfig.sidebarResizer,
      eventBus,
      this.l10n
    );
  },
  run(config) {
    this.initialize(config).then(webViewerInitialized);
  },
  get initialized() {