  - Open https://mozilla.github.io/pdf.js/web/viewer.html
  - Open a pdf with some XFA (for example the on in https://github.com/mozilla/pdf.js/issues/13679#issue-937616350)

The pdf is not correctly displayed because `enableXfa` is false.

@Snuffleupagus, the pref is set to true in Firefox nightly, is there anything blocking setting it to true in the web viewer ?  
},
  maxImageSize: {
    
    value: -1,
    kind: OptionKind.API,
  },
  pdfBug: {
    
    value: false,
    kind: OptionKind.API,
  },
  standardFontDataUrl: {
    
    value:
      typeof PDFJSDev === "undefined" || !PDFJSDev.test("PRODUCTION")
        ? "../external/standard_fonts/"
        : "../web/standard_fonts/",
    kind: OptionKind.API,
  },
  verbosity: {
    
    value: 1,
    kind: OptionKind.API,
  },
  workerPort: {
    
    value: null,
    kind: OptionKind.WORKER,
  },
  workerSrc: {