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)


this._nextPage(task, 'Expected "other" test-case to be linked.');
            return;
          }
          this.currentTask++;
          this._nextTask();
          return;
        }
        this._log('Loading file "' + task.file + '"\n');
        const absoluteUrl = new URL(task.file, window.location).href;
        try {
          let xfaStyleElement = null;
          if (task.enableXfa) {
            
            
            
            xfaStyleElement = document.createElement("style");
            document.documentElement
              .getElementsByTagName("head")[0]
              .appendChild(xfaStyleElement);
          }
          const loadingTask = pdfjsLib.getDocument({
            url: absoluteUrl,
            password: task.password,
            cMapUrl: CMAP_URL,
            cMapPacked: CMAP_PACKED,
            standardFontDataUrl: STANDARD_FONT_DATA_URL,
            disableRange: task.disableRange,
            disableAutoFetch: !task.enableAutoFetch,
            pdfBug: true,
            useSystemFonts: task.useSystemFonts,