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.
switch (evt.action) {
    case "GoToPage":
      PDFViewerApplication.appConfig.toolbar.pageNumber.select();
      break;
    case "Find":
      if (!PDFViewerApplication.supportsIntegratedFind) {
        PDFViewerApplication.findBar.toggle();
      }
      break;
    case "Print":
      PDFViewerApplication.triggerPrinting();
      break;
    case "SaveAs":
      webViewerSave();
      break;
  }
}
function webViewerPresentationModeChanged(evt) {