  - 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 ?  
* distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
"use strict";
if (!pdfjsLib.getDocument || !pdfjsViewer.PDFViewer) {
  
  alert("Please build the pdfjs-dist library using\n  `gulp dist-install`");
}
pdfjsLib.GlobalWorkerOptions.workerSrc =
  "../../node_modules/pdfjs-dist/build/pdf.worker.js";
const CMAP_URL = "../../node_modules/pdfjs-dist/cmaps/";
const CMAP_PACKED = true;
const DEFAULT_URL = "../../web/compressed.tracemonkey-pldi-09.pdf";
const SEARCH_FOR = ""; 
const SANDBOX_BUNDLE_SRC = "../../node_modules/pdfjs-dist/build/pdf.sandbox.js";
const container = document.getElementById("viewerContainer");
const eventBus = new pdfjsViewer.EventBus();
const pdfLinkService = new pdfjsViewer.PDFLinkService({
  eventBus,
});
const pdfFindController = new pdfjsViewer.PDFFindController({
  eventBus,
  linkService: pdfLinkService,
});
const pdfScriptingManager = new pdfjsViewer.PDFScriptingManager({
  eventBus,
  sandboxBundleSrc: SANDBOX_BUNDLE_SRC,
});