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)


styles = Object.values(styles);
  if (styles.every(style => style.promise)) {
    return Promise.all(styles.map(style => style.promise));
  }
  for (const style of styles) {
    style.promise = new Promise(function (resolve, reject) {
      const xhr = new XMLHttpRequest();
      xhr.open("GET", style.file);
      xhr.onload = function () {
        resolve(xhr.responseText);
      };
      xhr.onerror = function (e) {
        reject(new Error(`Error fetching style (${style.file}): ${e}`));
      };
      xhr.send(null);
    });
  }
  return Promise.all(styles.map(style => style.promise));
}
function writeSVG(svgElement, ctx, resolve, reject) {