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)


);
        task.pageNum++;
        self._nextPage(task);
      });
    },
    _quit: function Driver_quit() {
      this._log("Done !");
      this.end.textContent = "Tests finished. Close this window!";
      
      var r = new XMLHttpRequest();
      r.open("POST", `/tellMeToQuit?browser=${escape(this.browser)}`, false);
      r.onreadystatechange = function (e) {
        if (r.readyState === 4) {
          window.close();
        }
      };
      r.send(null);
    },
    _info: function Driver_info(message) {
      this._send(
        "/info",
        JSON.stringify({
          browser: this.browser,
          message,
        })
      );
    },
    _log: function Driver_log(message) {