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)


super(TEMPLATE_NS_ID, "text");
    this.id = attributes.id || "";
    this.maxChars = getInteger({
      data: attributes.maxChars,
      defaultValue: 0,
      validate: x => x >= 0,
    });
    this.name = attributes.name || "";
    this.rid = attributes.rid || "";
    this.use = attributes.use || "";
    this.usehref = attributes.usehref || "";
  }
  [$acceptWhitespace]() {
    return true;
  }
  [$onChild](child) {
    if (child[$namespaceId] === NamespaceIds.xhtml.id) {
      this[$content] = child;
      return true;
    }
    warn(`XFA - Invalid content in Text: ${child[$nodeName]}.`);
    return false;
  }
  [$onText](str) {
    if (this[$content] instanceof XFAObject) {
      return;
    }
    super[$onText](str);
  }
  [$toHTML](availableSpace) {