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.
return {
      id: this.data.id,
      value: this.data.fieldValue,
      defaultValue: this.data.defaultFieldValue,
      multiline: this.data.multiLine,
      password: this.hasFieldFlag(AnnotationFieldFlag.PASSWORD),
      charLimit: this.data.maxLen,
      comb: this.data.comb,
      editable: !this.data.readOnly,
      hidden: this.data.hidden,
      name: this.data.fieldName,
      rect: this.data.rect,
      actions: this.data.actions,
      type: "text",
    };
  }
}
class ButtonWidgetAnnotation extends WidgetAnnotation {