Attach (recommended) or Link to PDF file here:
https://guichet.public.lu/dam-assets/catalogue-formulaires/tva/tva-option-aic-pers-morales/tva-option-aic-pers-morale-DE.pdf

Configuration:
- Web browser and its version: Firefox Nightly 91.0a1 (2021-06-26) (64-bit)
- Operating system and its version: Windows 10.0.19043.1052
- PDF.js version: N/A

Steps to reproduce the problem:
1. enableXFA in Firefox Nightly
2. Open form

What is the expected behavior? (add screenshot)
Header image is scaled properly
![image](https://user-images.githubusercontent.com/7104454/123525954-905d1f00-d6a2-11eb-840e-be30eee395e1.png)

What went wrong? (add screenshot)
Image is scaled to fit
![image](https://user-images.githubusercontent.com/7104454/123525957-96530000-d6a2-11eb-9991-bf7f37c6f1a5.png)


"draw",
        "field",
        "exclGroup",
        "subform",
        "subformSet",
      ]),
      include: true,
    });
    if (!result.success) {
      if (result.isBreak()) {
        return result;
      }
      
      
      delete this[$extra];
      return HTMLResult.FAILURE;
    }
    style.width = measureToString(this[$extra].width);
    style.height = measureToString(this[$extra].height);
    const html = {
      name: "div",
      attributes,
      children,
    };
    const bbox = [this.x, this.y, this[$extra].width, this[$extra].height];
    delete this[$extra];
    return HTMLResult.success(html, bbox);
  }
}
class Assist extends XFAObject {