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)


return new Bookend(attrs);
  }
  static boolean(attrs) {
    return new BooleanElement(attrs);
  }
  static border(attrs) {
    return new Border(attrs);
  }
  static break(attrs) {
    return new Break(attrs);
  }
  static breakAfter(attrs) {
    return new BreakAfter(attrs);
  }
  static breakBefore(attrs) {
    return new BreakBefore(attrs);
  }
  static button(attrs) {
    return new Button(attrs);
  }
  static calculate(attrs) {
    return new Calculate(attrs);
  }
  static caption(attrs) {
    return new Caption(attrs);
  }
  static certificate(attrs) {
    return new Certificate(attrs);
  }
  static certificates(attrs) {