  - 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 ?  
enablePermissions: {
    
    value: false,
    kind: OptionKind.VIEWER + OptionKind.PREFERENCE,
  },
  enablePrintAutoRotate: {
    
    value: true,
    kind: OptionKind.VIEWER + OptionKind.PREFERENCE,
  },
  enableScripting: {
    
    value: typeof PDFJSDev === "undefined" || !PDFJSDev.test("CHROME"),
    kind: OptionKind.VIEWER + OptionKind.PREFERENCE,
  },
  externalLinkRel: {
    
    value: "noopener noreferrer nofollow",
    kind: OptionKind.VIEWER,
  },
  externalLinkTarget: {
    
    value: 0,
    kind: OptionKind.VIEWER + OptionKind.PREFERENCE,
  },
  historyUpdateUrl: {
    
    value: false,
    kind: OptionKind.VIEWER + OptionKind.PREFERENCE,
  },