  - 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 ?  
const options = Object.create(null);
    for (const name in defaultOptions) {
      const defaultOption = defaultOptions[name];
      if (kind) {
        if ((kind & defaultOption.kind) === 0) {
          continue;
        }
        if (kind === OptionKind.PREFERENCE) {
          const value = defaultOption.value,
            valueType = typeof value;
          if (
            valueType === "boolean" ||
            valueType === "string" ||
            (valueType === "number" && Number.isInteger(value))
          ) {
            options[name] = value;
            continue;
          }
          throw new Error(`Invalid type for preference: ${name}`);
        }
      }
      const userOption = userOptions[name];
      options[name] =
        userOption !== undefined
          ? userOption
          : defaultOption.compatibility ?? defaultOption.value;
    }
    return options;
  }
  static set(name, value) {