var ua = navigator.userAgent;

if (/Firefox\//.test(ua))
   var Firefox = /Firefox\/([0-9\.A-z]+)/.exec(ua)[1];

这让我有了火狐的版本，

    let versionNumber = parseInt(window.navigator.userAgent.match(/Firefox\/([0- 
    9]+)\./)[1]);

这个页面似乎有一个非常漂亮的代码片段，它只使用appString和appVersion属性作为最后的手段，因为它声称它们在某些浏览器中是不可靠的。 页面上的代码如下:

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;

// In Opera 15+, the true version is after "OPR/" 
if ((verOffset=nAgt.indexOf("OPR/"))!=-1) {
 browserName = "Opera";
 fullVersion = nAgt.substring(verOffset+4);
}
// In older Opera, the true version is after "Opera" or after "Version"
else if ((verOffset=nAgt.indexOf("Opera"))!=-1) {
 browserName = "Opera";
 fullVersion = nAgt.substring(verOffset+6);
 if ((verOffset=nAgt.indexOf("Version"))!=-1) 
   fullVersion = nAgt.substring(verOffset+8);
}
// In MSIE, the true version is after "MSIE" in userAgent
else if ((verOffset=nAgt.indexOf("MSIE"))!=-1) {
 browserName = "Microsoft Internet Explorer";
 fullVersion = nAgt.substring(verOffset+5);
}
// In Chrome, the true version is after "Chrome" 
else if ((verOffset=nAgt.indexOf("Chrome"))!=-1) {
 browserName = "Chrome";
 fullVersion = nAgt.substring(verOffset+7);
}
// In Safari, the true version is after "Safari" or after "Version" 
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);
}
// In Firefox, the true version is after "Firefox" 
else if ((verOffset=nAgt.indexOf("Firefox"))!=-1) {
 browserName = "Firefox";
 fullVersion = nAgt.substring(verOffset+8);
}
// In most other browsers, "name/version" is at the end of userAgent 
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 the fullVersion string at semicolon/space if present
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);
}

document.write(''
 +'Browser name  = '+browserName+'<br>'
 +'Full version  = '+fullVersion+'<br>'
 +'Major version = '+majorVersion+'<br>'
 +'navigator.appName = '+navigator.appName+'<br>'
 +'navigator.userAgent = '+navigator.userAgent+'<br>'
)

<script type="text/javascript">
var version = navigator.appVersion;
alert(version);
</script>

使用这个:http://www.quirksmode.org/js/detect.html

alert(BrowserDetect.browser); // will say "Firefox"
alert(BrowserDetect.version); // will say "3" or "4"

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;

// In Opera 15+, the true version is after "OPR/" 
if ((verOffset = nAgt.indexOf("OPR/")) != -1) {
    browserName = "Opera";
    fullVersion = nAgt.substring(verOffset + 4);
}
// In older Opera, the true version is after "Opera" or after "Version"
else if ((verOffset = nAgt.indexOf("Opera")) != -1) {
    browserName = "Opera";
    fullVersion = nAgt.substring(verOffset + 6);
    if ((verOffset = nAgt.indexOf("Version")) != -1)
        fullVersion = nAgt.substring(verOffset + 8);
}
// In MSIE, the true version is after "MSIE" in userAgent
else if ((verOffset = nAgt.indexOf("MSIE")) != -1) {
    browserName = "Microsoft Internet Explorer";
    fullVersion = nAgt.substring(verOffset + 5);
}
// In Chrome, the true version is after "Chrome" 
else if ((verOffset = nAgt.indexOf("Chrome")) != -1) {
    browserName = "Google Chrome";
    fullVersion = nAgt.substring(verOffset + 7);
}
// In Safari, the true version is after "Safari" or after "Version" 
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);
}
// In Firefox, the true version is after "Firefox" 
else if ((verOffset = nAgt.indexOf("Firefox")) != -1) {
    browserName = "Mozilla Firefox";
    fullVersion = nAgt.substring(verOffset + 8);
}
// In most other browsers, "name/version" is at the end of userAgent 
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 the fullVersion string at semicolon/space if present
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);
}