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 isPdfData = isPdfFile(filename);
    const contentType = isPdfData ? "application/pdf" : "";
    if (isPdfData && !compatibilityParams.disableCreateObjectURL) {
      let blobUrl = this._openBlobUrls.get(element);
      if (!blobUrl) {
        blobUrl = URL.createObjectURL(new Blob([data], { type: contentType }));
        this._openBlobUrls.set(element, blobUrl);
      }
      let viewerUrl;
      if (typeof PDFJSDev === "undefined" || PDFJSDev.test("GENERIC")) {
        
        viewerUrl = "?file=" + encodeURIComponent(blobUrl + "#" + filename);
      } else if (PDFJSDev.test("CHROME")) {
        
        
        viewerUrl =
          
          chrome.runtime.getURL("/content/web/viewer.html") +
          "?file=" +
          encodeURIComponent(blobUrl + "#" + filename);
      }
      try {
        window.open(viewerUrl);