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 cl = layoutClass(this);
    if (cl) {
      classNames.push(cl);
    }
    if (isPrintOnly(this)) {
      classNames.push("xfaPrintOnly");
    }
    attributes.style = style;
    attributes.class = classNames;
    if (this.name) {
      attributes.xfaName = this.name;
    }
    let failure;
    if (this.layout === "lr-tb" || this.layout === "rl-tb") {
      for (
        ;
        this[$extra].attempt < MAX_ATTEMPTS_FOR_LRTB_LAYOUT;
        this[$extra].attempt++
      ) {
        const result = this[$childrenToHTML]({
          filter,
          include: true,
        });
        if (result.success) {
          break;
        }
        if (result.isBreak()) {
          return result;
        }
      }