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)


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        style.background = color;
        style.backgroundClip = "text";
        style.color = "transparent";
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    }
    if (this.baselineShift) {
      style.verticalAlign = measureToString(this.baselineShift);
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    style.fontKerning = this.kerningMode === "none" ? "none" : "normal";
    style.letterSpacing = measureToString(this.letterSpacing);
    if (this.lineThrough !== 0) {
      style.textDecoration = "line-through";