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)


let maxRun =
      this.layout === "lr-tb" || this.layout === "rl-tb"
        ? MAX_ATTEMPTS_FOR_LRTB_LAYOUT
        : 1;
    maxRun += !isSplittable && this.layout !== "position" ? 1 : 0;
    for (; this[$extra].attempt < maxRun; this[$extra].attempt++) {
      const result = this[$childrenToHTML]({
        filter,
        include: true,
      });
      if (result.success) {
        break;
      }
      if (result.isBreak()) {
        return result;
      }
    }
    if (this[$extra].attempt === maxRun) {
      if (this.overflow) {
        this[$getTemplateRoot]()[$extra].overflowNode = this.overflow;
      }
      if (!isSplittable) {
        
        
        delete this[$extra];
      }
      return HTMLResult.FAILURE;
    }
    let marginH = 0;