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 FONT_FACTOR = 0.8;
      if (lineCount === -1) {
        fontSize = roundWithOneDigit(FONT_FACTOR * height);
      } else {
        
        
        
        
        
        
        
        fontSize = 10;
        let lineHeight = fontSize / FONT_FACTOR;
        let numberOfLines = Math.round(height / lineHeight);
        numberOfLines = Math.max(numberOfLines, lineCount);
        lineHeight = height / numberOfLines;
        fontSize = roundWithOneDigit(FONT_FACTOR * lineHeight);
      }
      const { fontName, fontColor } = this.data.defaultAppearanceData;
      this._defaultAppearance = createDefaultAppearance({
        fontSize,
        fontName,
        fontColor,
      });
    }
    return [this._defaultAppearance, fontSize];
  }
  _renderText(text, font, fontSize, totalWidth, alignment, hPadding, vPadding) {