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)


constructor(attributes) {
    super(TEMPLATE_NS_ID, "encryptionMethods",  true);
    this.id = attributes.id || "";
    this.type = getStringOption(attributes.type, ["optional", "required"]);
    this.use = attributes.use || "";
    this.usehref = attributes.usehref || "";
    this.encryptionMethod = new XFAObjectArray();
  }
}
class Event extends XFAObject {
  constructor(attributes) {
    super(TEMPLATE_NS_ID, "event",  true);
    this.activity = getStringOption(attributes.activity, [
      "click",
      "change",
      "docClose",
      "docReady",
      "enter",
      "exit",
      "full",
      "indexChange",
      "initialize",
      "mouseDown",
      "mouseEnter",
      "mouseExit",
      "mouseUp",
      "postExecute",
      "postOpen",
      "postPrint",
      "postSave",