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 (
      info.IsXFAPresent &&
      !info.IsAcroFormPresent &&
      
      !pdfDocument.isPureXfa
    ) {
      console.warn("Warning: XFA support is not enabled");
      this.fallback(UNSUPPORTED_FEATURES.forms);
    } else if (
      (info.IsAcroFormPresent || info.IsXFAPresent) &&
      !this.pdfViewer.renderForms
    ) {
      console.warn("Warning: Interactive form support is not enabled");
      this.fallback(UNSUPPORTED_FEATURES.forms);
    }
    if (info.IsSignaturesPresent) {
      console.warn("Warning: Digital signatures validation is not supported");
      this.fallback(UNSUPPORTED_FEATURES.signatures);
    }
    
    let versionId = "other";
    if (KNOWN_VERSIONS.includes(info.PDFFormatVersion)) {
      versionId = `v${info.PDFFormatVersion.replace(".", "_")}`;
    }
    let generatorId = "other";
    if (info.Producer) {
      const producer = info.Producer.toLowerCase();
      KNOWN_GENERATORS.some(function (generator) {
        if (!producer.includes(generator)) {
          return false;