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)


this.desc = null;
    this.extras = null;
    this.font = null;
    this.keep = null;
    this.margin = null;
    this.para = null;
    this.traversal = null;
    this.ui = null;
    this.value = null;
    this.setProperty = new XFAObjectArray();
  }
  [$setValue](value) {
    _setValue(this, value);
  }
  [$toHTML](availableSpace) {
    if (this.presence === "hidden" || this.presence === "inactive") {
      return HTMLResult.EMPTY;
    }
    fixDimensions(this);
    if ((this.w === "" || this.h === "") && this.value) {
      let marginH = 0;
      let marginV = 0;
      if (this.margin) {
        marginH = this.margin.leftInset + this.margin.rightInset;
        marginV = this.margin.topInset + this.margin.bottomInset;
      }
      const maxWidth = this.w === "" ? availableSpace.width : this.w;
      const fontFinder = this[$globalData].fontFinder;
      let font = this.font;
      if (!font) {