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.
case "Ink":
        return new InkAnnotation(parameters);
      case "Highlight":
        return new HighlightAnnotation(parameters);
      case "Underline":
        return new UnderlineAnnotation(parameters);
      case "Squiggly":
        return new SquigglyAnnotation(parameters);
      case "StrikeOut":
        return new StrikeOutAnnotation(parameters);
      case "Stamp":
        return new StampAnnotation(parameters);
      case "FileAttachment":
        return new FileAttachmentAnnotation(parameters);
      default:
        if (!collectFields) {
          if (!subtype) {
            warn("Annotation is missing the required /Subtype.");
          } else {
            warn(
              `Unimplemented annotation type "${subtype}", ` +
                "falling back to base annotation."
            );
          }
        }
        return new Annotation(parameters);
    }
  }
}
function getRgbColor(color) {