Deciphering Your Fx User Agent

Your Firefox User Agent or build ID contains a lot of information about your browser as well as your operating system. Here is break down on what is in your User Agent:

Mozilla/MozVer (Platform; Security; SubPlatform; Language; rv:Revision[; Extension]*) Gecko/GeckVer [Product/ProdVer]

  • Mozilla/MozVer ~ All Firefox build IDs start with Mozilla/5.0. Simply put this means the browser meets the standards to be Netscape 5 compatible. This was the first Mozilla based (never released) version of Netscape.
  • Platform ~ This is the operating system (but not the version). Possible values include:
    • Windows
    • Macintosh
    • X11 (Linux)
  • Security ~ This is the encryption strength of the browser:
    • U: Strong Security, 128-bit encryption (USA)
    • I: Weak Security, 40-bit encryption (International)
    • N: No Security, No encryption
  • SubPlatform ~ This is the version of the operating system.
    • Windows:
      • Win 3.11 – Windows 3.11
      • Win 95 – Windows 95
      • Win 98 – Windows 98
      • Win 9X – Windows ME
      • Win NT 4.0 – Windows NT 4.0
      • Win NT 5.0 – Windows 2000
      • Win NT 5.1 – Windows XP
      • Win NT 5.2 – Windows Server 2003 and XP Pro x64
      • Win NT 6.0 – Windows Vista
    • x11 Linux:
      • Linux [Version] Hardware
      • FreeBSD Hardware
      • NetBSD Hardware
      • SunOS sun4u
    • Macintosh:
      • PPC Mac OS X
      • PPC Mac OS X Mach-O
      • Intel Mac OS X
  • Language ~ standardized language identifier, Firefox is available in several different languages. The two common English language builds are:
    • en-US = English United States.
    • en-GB =English Great Britain.
  • rv:Revision ~ This is the version of Gecko, the browser engine.
  • Gecko/GeckoVer ~ This is the date in YYYYMMDD format the revision (or version) of Gecko was was compiled, not necessarily the date it was released
  • Product/ProdVer ~ The name and version of the product. Some of these include:
    • Deer Park/1.5
    • BonEcho/
    • Firefox/
    • Firefox/
    • Gran Paradiso/3.0a1
    • Minefield/3.0a2

Below is the user agent as found via Help, About Mozilla Firefox for my current version of Firefox:

Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv: Gecko/20061223 BonEcho/

I am running a Mozilla product compilable with Netscape 5.0, on a Windows platform, with high 128-bit encryption USA security, on the Windows NT 5.1 (XP) subplatform, using an english-US language. My current build of Firefox is based on the revision of Gecko which was compiled on 12/23/2006. The product name is BonEcho (nightly build) and the version I am running is

Now you can see how valuable your user agent/build ID is for troubleshooting, especially when people are not even sure what operating system they are using much less which version of Firefox.

Source: Wikipedia