Attach (recommended) or Link to PDF file here:
http://help.adobe.com/en_US/livecycle/11.0/SampleForms/941/Form.pdf

- Web browser and its version: Firefox 89.0.1
- Operating system and its version: Windows 10 10.0.19043.1052
- PDF.js version: commit bdfcdd6f8326f22c135edfa29a341ea4c558f3d1
- Is a browser extension: No

Steps to reproduce the problem:
1. Enable XFA support
2. Open form

What is the expected behavior? (add screenshot)
Page 3 (of 4) renders
![image](https://user-images.githubusercontent.com/7104454/122686842-622e9980-d1e1-11eb-92ab-86fe488560f2.png)

What went wrong? (add screenshot)
Only 3 pages total render in pdf.js
return this.defaultFont;
  }
  find(fontName, mustWarn = true) {
    let font = this.fonts.get(fontName) || this.cache.get(fontName);
    if (font) {
      return font;
    }
    const pattern = /,|-| |bolditalic|bold|italic|regular|it/gi;
    let name = fontName.replace(pattern, "");
    font = this.fonts.get(name);
    if (font) {
      this.cache.set(fontName, font);
      return font;
    }
    name = name.toLowerCase();
    const maybe = [];
    for (const [family, pdfFont] of this.fonts.entries()) {
      if (family.replace(pattern, "").toLowerCase().startsWith(name)) {
        maybe.push(pdfFont);
      }
    }
    if (maybe.length === 0) {