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)


const style = toStyle(this, "hAlign");
    if (this.marginLeft !== "") {
      style.marginLeft = measureToString(this.marginLeft);
    }
    if (this.marginRight !== "") {
      style.marginRight = measureToString(this.marginRight);
    }
    if (this.spaceAbove !== "") {
      style.marginTop = measureToString(this.spaceAbove);
    }
    if (this.spaceBelow !== "") {
      style.marginBottom = measureToString(this.spaceBelow);
    }
    if (this.textIndent !== "") {
      style.textIndent = measureToString(this.textIndent);
      fixTextIndent(style);
    }
    if (this.lineHeight > 0) {
      style.lineHeight = measureToString(this.lineHeight);
    }