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)


run: function Driver_run() {
      var self = this;
      window.onerror = function (message, source, line, column, error) {
        self._info(
          "Error: " +
            message +
            " Script: " +
            source +
            " Line: " +
            line +
            " Column: " +
            column +
            " StackTrace: " +
            error
        );
      };
      this._info("User agent: " + navigator.userAgent);
      this._log(`Harness thinks this browser is ${this.browser}\n`);
      this._log('Fetching manifest "' + this.manifestFile + '"... ');
      var r = new XMLHttpRequest();
      r.open("GET", this.manifestFile, false);
      r.onreadystatechange = function () {
        if (r.readyState === 4) {
          self._log("done\n");
          self.manifest = JSON.parse(r.responseText);
          if (self.testFilter && self.testFilter.length) {
            self.manifest = self.manifest.filter(function (item) {
              return self.testFilter.includes(item.id);
            });
          }