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)


return loadStyles(styles);
  }
  
  function rasterizeXfaLayer(ctx, viewport, xfa, fontRules) {
    return new Promise(function (resolve, reject) {
      
      const svg = document.createElementNS(SVG_NS, "svg:svg");
      svg.setAttribute("width", viewport.width + "px");
      svg.setAttribute("height", viewport.height + "px");
      const foreignObject = document.createElementNS(
        SVG_NS,
        "svg:foreignObject"
      );
      foreignObject.setAttribute("x", "0");
      foreignObject.setAttribute("y", "0");
      foreignObject.setAttribute("width", viewport.width + "px");
      foreignObject.setAttribute("height", viewport.height + "px");
      const style = document.createElement("style");
      const stylePromise = getXfaLayerStyle();
      foreignObject.appendChild(style);
      const div = document.createElement("div");
      foreignObject.appendChild(div);
      stylePromise
        .then(async cssRules => {
          style.textContent = fontRules + "\n" + cssRules;
          pdfjsLib.XfaLayer.render({
            xfa,
            div,
            viewport: viewport.clone({ dontFlip: true }),