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.
const numLabels = labels.length;
    if (numLabels !== this.pagesCount) {
      console.error(
        "The number of Page Labels does not match the number of pages in the document."
      );
      return;
    }
    let i = 0;
    
    while (i < numLabels && labels[i] === (i + 1).toString()) {
      i++;
    }
    if (i === numLabels) {
      return;
    }
    const { pdfViewer, pdfThumbnailViewer, toolbar } = this;
    pdfViewer.setPageLabels(labels);
    pdfThumbnailViewer.setPageLabels(labels);
    
    
    toolbar.setPagesCount(numLabels, true);
    toolbar.setPageNumber(
      pdfViewer.currentPageNumber,
      pdfViewer.currentPageLabel
    );
  },
  /**
   * @private
   */
  _initializePdfHistory({ fingerprint, viewOnLoad, initialDest = null }) {