Attach (recommended) or Link to PDF file here:
[output.pdf](https://github.com/mozilla/pdf.js/files/6374987/output.pdf)

Configuration:
- Web browser and its version: Firefox 88.0
- Operating system and its version: macOS Big Sur 11.2.3 (20D91)
- PDF.js version: 2.8.243
- Is a browser extension: no/Firefox built-in

Steps to reproduce the problem:
1.  add Ink-Annotations to a pdf (i use https://github.com/highkite/pdfAnnotate, Annotations with appearance streams are shown correctly)
2. open output file in firefox

What is the expected behavior? 
The annotations should be visible.
![Bildschirmfoto 2021-04-26 um 09 15 48](https://user-images.githubusercontent.com/33630884/116043809-6a020f80-a670-11eb-973c-6f2df3dae532.png)

What went wrong? 
The annotations are added to the dom but invisible.
![Bildschirmfoto 2021-04-26 um 09 18 26](https://user-images.githubusercontent.com/33630884/116043867-7e460c80-a670-11eb-964d-0cc2c6dbfb61.png)

Tested successfull with FoxitReader, AcrobatReader, Chrome and Safari.
}
      let appearance;
      if (value) {
        appearance = this.checkedAppearance;
      } else {
        appearance = this.uncheckedAppearance;
      }
      if (appearance) {
        const savedAppearance = this.appearance;
        this.appearance = appearance;
        const operatorList = super.getOperatorList(
          evaluator,
          task,
          renderForms,
          annotationStorage
        );
        this.appearance = savedAppearance;
        return operatorList;
      }
      
      return Promise.resolve(new OperatorList());
    }
    return super.getOperatorList(
      evaluator,
      task,
      renderForms,
      annotationStorage
    );
  }
  async save(evaluator, task, annotationStorage) {