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)


if (this.lineThrough === 2) {
        style.textDecorationStyle = "double";
      }
    }
    
    if (this.overline !== 0) {
      style.textDecoration = "overline";
      if (this.overline === 2) {
        style.textDecorationStyle = "double";
      }
    }
    
    style.fontStyle = this.posture;
    const fontSize = measureToString(0.99 * this.size);
    if (fontSize !== "10px") {
      style.fontSize = fontSize;
    }
    setFontFamily(this, this[$globalData].fontFinder, style);
    if (this.underline !== 0) {
      style.textDecoration = "underline";
      if (this.underline === 2) {
        style.textDecorationStyle = "double";
      }
    }
    
    style.fontWeight = this.weight;
    return style;
  }
}
class Format extends XFAObject {