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.
const customAppearance = params.dict.get("AP");
    if (!isDict(customAppearance)) {
      return;
    }
    const normalAppearance = customAppearance.get("N");
    if (!isDict(normalAppearance)) {
      return;
    }
    const exportValues = normalAppearance.getKeys();
    if (!exportValues.includes("Off")) {
      
      exportValues.push("Off");
    }
    if (exportValues.length !== 2) {
      return;
    }
    this.data.exportValue =
      exportValues[0] === "Off" ? exportValues[1] : exportValues[0];
    this.checkedAppearance = normalAppearance.get(this.data.exportValue);
    this.uncheckedAppearance = normalAppearance.get("Off") || null;
    this._streams.push(this.checkedAppearance);
    if (this.uncheckedAppearance) {
      this._streams.push(this.uncheckedAppearance);
    }
    this._fallbackFontDict = this.fallbackFontDict;
  }
  _processRadioButton(params) {