Follow up with issue: https://github.com/mozilla/pdf.js/issues/14146
Merged pull req: https://github.com/mozilla/pdf.js/pull/14189

Attach (recommended) or Link to PDF file here:
https://bug1708641.bmoattachments.org/attachment.cgi?id=9219459

- This popup appears because JS is enabled;
- And because the pdf contains some unsupported features (e.g. XFA);

Configuration:
- Firefox Nightly & Chrome
- macOS Big Sur 11.6

Steps to reproduce the problem:
1. Run gulp server
2. Open attached pdf

What is the expected behavior? 
No popup on open

What went wrong?
![error](https://user-images.githubusercontent.com/76935202/139354112-707887a2-a6a1-43a9-a92e-45d57c48206a.jpg)



this._unregisterTimeoutCallback(callbackId);
    if (interval) {
      this._externalCall("clearInterval", [callbackId]);
    } else {
      this._externalCall("clearTimeout", [callbackId]);
    }
  }
  static _getPlatform(platform) {
    if (typeof platform === "string") {
      platform = platform.toLowerCase();
      if (platform.includes("win")) {
        return "WIN";
      } else if (platform.includes("mac")) {
        return "MAC";
      }
    }
    return "UNIX";
  }
  static _getLanguage(language) {
    const [main, sub] = language.toLowerCase().split(/[-_]/);
    switch (main) {
      case "zh":
        if (sub === "cn" || sub === "sg") {
          return "CHS";
        }
        return "CHT";
      case "da":
        return "DAN";