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 (PDFViewerApplication.supportsIntegratedFind) {
    PDFViewerApplication.externalServices.updateFindMatchesCount(matchesCount);
  } else {
    PDFViewerApplication.findBar.updateResultsCount(matchesCount);
  }
}
function webViewerUpdateFindControlState({
  state,
  previous,
  matchesCount,
  rawQuery,
}) {
  if (PDFViewerApplication.supportsIntegratedFind) {
    PDFViewerApplication.externalServices.updateFindControlState({
      result: state,
      findPrevious: previous,
      matchesCount,
      rawQuery,
    });
  } else {
    PDFViewerApplication.findBar.updateUIState(state, previous, matchesCount);
  }
}
function webViewerScaleChanging(evt) {
  PDFViewerApplication.toolbar.setPageScale(evt.presetValue, evt.scale);
  PDFViewerApplication.pdfViewer.update();
}
function webViewerRotationChanging(evt) {