Attach (recommended) or Link to PDF file here:
http://help.adobe.com/en_US/livecycle/11.0/SampleForms/941/Form.pdf

- Web browser and its version: Firefox 89.0.1
- Operating system and its version: Windows 10 10.0.19043.1052
- PDF.js version: commit bdfcdd6f8326f22c135edfa29a341ea4c558f3d1
- Is a browser extension: No

Steps to reproduce the problem:
1. Enable XFA support
2. Open form

What is the expected behavior? (add screenshot)
Page 3 (of 4) renders
![image](https://user-images.githubusercontent.com/7104454/122686842-622e9980-d1e1-11eb-92ab-86fe488560f2.png)

What went wrong? (add screenshot)
Only 3 pages total render in pdf.js
this.xref.setStartXRef(this.startXRef);
  }
  get numPages() {
    if (this.xfaFactory) {
      return shadow(this, "numPages", this.xfaFactory.numberPages);
    }
    const linearization = this.linearization;
    const num = linearization ? linearization.numPages : this.catalog.numPages;
    return shadow(this, "numPages", num);
  }
  /**
   * @private
   */
  _hasOnlyDocumentSignatures(fields, recursionDepth = 0) {