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.
case 74: 
      case 78: 
        turnPage = 1;
        break;
      case 36: 
        if (isViewerInPresentationMode || PDFViewerApplication.page > 1) {
          PDFViewerApplication.page = 1;
          handled = true;
          ensureViewerFocused = true;
        }
        break;
      case 35: 
        if (
          isViewerInPresentationMode ||
          PDFViewerApplication.page < PDFViewerApplication.pagesCount
        ) {
          PDFViewerApplication.page = PDFViewerApplication.pagesCount;
          handled = true;
          ensureViewerFocused = true;
        }
        break;
      case 83: 
        PDFViewerApplication.pdfCursorTools.switchTool(CursorTool.SELECT);
        break;
      case 72: 
        PDFViewerApplication.pdfCursorTools.switchTool(CursorTool.HAND);
        break;
      case 82: 
        PDFViewerApplication.rotatePages(90);