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 (typeof PDFJSDev === "undefined" || PDFJSDev.test("GENERIC")) {
    if (file) {
      PDFViewerApplication.open(file);
    }
  } else if (PDFJSDev.test("MOZCENTRAL || CHROME")) {
    PDFViewerApplication.setTitleUsingUrl(file);
    PDFViewerApplication.initPassiveLoading();
  } else {
    if (file) {
      throw new Error("Not implemented: webViewerOpenFileViaURL");
    }
  }
}
function webViewerResetPermissions() {
  const { appConfig } = PDFViewerApplication;
  if (!appConfig) {
    return;
  }
  
  appConfig.viewerContainer.classList.remove(ENABLE_PERMISSIONS_CLASS);
}
function webViewerPageRendered({ pageNumber, timestamp, error }) {
  
  
  if (pageNumber === PDFViewerApplication.page) {
    PDFViewerApplication.toolbar.updateLoadingIndicatorState(false);
  }