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.
pdfViewer: null,
  
  pdfThumbnailViewer: null,
  
  pdfRenderingQueue: null,
  
  pdfPresentationMode: null,
  
  pdfDocumentProperties: null,
  
  pdfLinkService: null,
  
  pdfHistory: null,
  
  pdfSidebar: null,
  
  pdfSidebarResizer: null,
  
  pdfOutlineViewer: null,
  
  pdfAttachmentViewer: null,
  
  pdfLayerViewer: null,
  
  pdfCursorTools: null,
  
  pdfScriptingManager: null,
  
  store: null,