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)


if (this.subform.children.length === 0) {
      warn("XFA - No subforms in template node.");
    }
    if (this.subform.children.length >= 2) {
      warn("XFA - Several subforms in template node: please file a bug.");
    }
  }
  [$searchNode](expr, container) {
    if (expr.startsWith("#")) {
      
      return [this[$ids].get(expr.slice(1))];
    }
    return searchNode(this, container, expr, true, true);
  }
  [$toHTML]() {
    if (!this.subform.children.length) {
      return HTMLResult.success({
        name: "div",
        children: [],
      });
    }
    this[$extra] = {
      overflowNode: null,
      pageNumber: 1,
      pagePosition: "first",
      oddOrEven: "odd",
      blankOrNotBlank: "nonBlank",
    };
    const root = this.subform.children[0];
    root.pageSet[$cleanPage]();