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)


addHTML(this, html, bbox);
  }
  [$getAvailableSpace]() {
    return getAvailableSpace(this);
  }
  [$toHTML](availableSpace) {
    if (
      this.presence === "hidden" ||
      this.presence === "inactive" ||
      this.h === 0 ||
      this.w === 0
    ) {
      return HTMLResult.EMPTY;
    }
    fixDimensions(this);
    const children = [];
    const attributes = {
      id: this[$uid],
      class: [],
    };
    setAccess(this, attributes.class);
    if (!this[$extra]) {
      this[$extra] = Object.create(null);
    }
    Object.assign(this[$extra], {
      children,
      attributes,
      attempt: 0,
      availableSpace,
      width: 0,