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)


startColor = startColor ? startColor[$toStyle]() : "#FFFFFF";
    const endColor = this.color ? this.color[$toStyle]() : "#000000";
    const width = 5;
    const cmd = "repeating-linear-gradient";
    const colors = `${startColor},${startColor} ${width}px,${endColor} ${width}px,${endColor} ${
      2 * width
    }px`;
    switch (this.type) {
      case "crossHatch":
        return `${cmd}(to top,${colors}) ${cmd}(to right,${colors})`;
      case "crossDiagonal":
        return `${cmd}(45deg,${colors}) ${cmd}(-45deg,${colors})`;
      case "diagonalLeft":
        return `${cmd}(45deg,${colors})`;
      case "diagonalRight":
        return `${cmd}(-45deg,${colors})`;
      case "horizontal":
        return `${cmd}(to top,${colors})`;
      case "vertical":
        return `${cmd}(to right,${colors})`;
    }
    return "";
  }
}
class Picture extends StringObject {