JavaScript를 사용하여 Internet Explorer 6에서 Firefox 버전 정보를 추출하려면 어떻게 해야 합니까?

var nVer = navigator.appVersion;
var nAgt = navigator.userAgent;
var browserName = navigator.appName;
var fullVersion = '' + parseFloat(navigator.appVersion);
var majorVersion = parseInt(navigator.appVersion, 10);
var nameOffset, verOffset, ix;

// Check for specific browsers
if ((verOffset = nAgt.indexOf("OPR")) != -1) {
  browserName = "Opera";
  fullVersion = nAgt.substring(verOffset + 4);
  if ((verOffset = nAgt.indexOf("Version")) != -1)
    fullVersion = nAgt.substring(verOffset + 8);
} else if ((verOffset = nAgt.indexOf("Edg")) != -1) {
  browserName = "Microsoft Edge";
  fullVersion = nAgt.substring(verOffset + 4);
} else if ((verOffset = nAgt.indexOf("MSIE")) != -1) {
  browserName = "Microsoft Internet Explorer";
  fullVersion = nAgt.substring(verOffset + 5);
} else if ((verOffset = nAgt.indexOf("Chrome")) != -1) {
  browserName = "Chrome";
  fullVersion = nAgt.substring(verOffset + 7);
} else if ((verOffset = nAgt.indexOf("Safari")) != -1) {
  browserName = "Safari";
  fullVersion = nAgt.substring(verOffset + 7);
  if ((verOffset = nAgt.indexOf("Version")) != -1)
    fullVersion = nAgt.substring(verOffset + 8);
} else if ((verOffset = nAgt.indexOf("Firefox")) != -1) {
  browserName = "Firefox";
  fullVersion = nAgt.substring(verOffset + 8);
} else if (
  (nameOffset = nAgt.lastIndexOf(" ") + 1) < (verOffset = nAgt.lastIndexOf("/"))
) {
  browserName = nAgt.substring(nameOffset, verOffset);
  fullVersion = nAgt.substring(verOffset + 1);
  if (browserName.toLowerCase() == browserName.toUpperCase()) {
    browserName = navigator.appName;
  }
}

// Trim version string
if ((ix = fullVersion.indexOf(";")) != -1) fullVersion = fullVersion.substring(0, ix);
if ((ix = fullVersion.indexOf(" ")) != -1) fullVersion = fullVersion.substring(0, ix);

majorVersion = parseInt('' + fullVersion, 10);
if (isNaN(majorVersion)) {
  fullVersion = '' + parseFloat(navigator.appVersion);
  majorVersion = parseInt(navigator.appVersion, 10);
}