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)


if (task.pageNum > this._getLastPageNumber(task)) {
        if (++task.round < task.rounds) {
          this._log(" Round " + (1 + task.round) + "\n");
          task.pageNum = task.firstPage || 1;
        } else {
          this.currentTask++;
          this._nextTask();
          return;
        }
      }
      if (task.skipPages && task.skipPages.includes(task.pageNum)) {
        this._log(
          " Skipping page " +
            task.pageNum +
            "/" +
            task.pdfDoc.numPages +
            "...\n"
        );
        task.pageNum++;
        this._nextPage(task);
        return;
      }
      if (!failure) {
        try {
          this._log(
            " Loading page " +
              task.pageNum +
              "/" +
              task.pdfDoc.numPages +
              "... "