Latest Firefox 21 user agents:

User Agent Platform Device
Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:21.0) Gecko/20100101 Firefox/21.0 Ubuntu Unknown
Mozilla/5.0 (X11; Ubuntu; Linux x8664; rv:21.0) Gecko/20100101 Firefox/21.0 Ubuntu Unknown
Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:21.0) Gecko/20100101 Firefox/21.0 Ubuntu Unknown
Mozilla/5.0 (X11; OpenBSD amd64; Linux x86_64; rv:21.0) Gecko/20130331 Firefox/21.0 OpenBSD Unknown
Mozilla/5.0 (X11; Linux x86_64; rv:21.0) Gecko/20100101 Firefox/21.0 GNU/Linux Unknown
Mozilla/5.0 (X11; Linux i686; rv:21.0) Gecko/20100101 Firefox/21.0) GNU/Linux Unknown
Mozilla/5.0 (X11; FreeBSD x86_64; rv:21.0) Gecko/21.0 Firefox/21.0 FreeBSD Unknown
Mozilla/5.0 (X11; FreeBSD amd64; rv:21.0) Gecko/20130331 Firefox/21.0 FreeBSD Unknown
Mozilla/5.0 (X11; FreeBSD amd64; rv:21.0) Gecko/20100101 Firefox/21.0 FreeBSD Unknown
Mozilla/5.0 (X11; FreeBSD amd64; Linux x86_64; rv:21.0) Gecko/20130331 Firefox/21.0 FreeBSD Unknown
Mozilla/5.0 (Windows; U; Windows NT 6.1; en-GB; rv:1.9.2.13) Gecko/20101203 Firefox/21 Windows 7 Unknown
Mozilla/5.0 (Windows NT.6.2; WOW64) Gecko/20061007 Firefox/21.0 Windows NT Unknown
Mozilla/5.0 (Windows NT.6.2; WOW64) Gecko/20031202 Firefox/21.0 Windows NT Unknown
Mozilla/5.0 (Windows NT.6.2; Win64; x64) Gecko/20101104 Firefox/21.0 Windows NT Unknown
Mozilla/5.0 (Windows NT.6.2; Win64; x64) Gecko/20100305 Firefox/21.0 Windows NT Unknown
Mozilla/5.0 (Windows NT.6.2; Win64; x64) Gecko/20030208 Firefox/21.0 Windows NT Unknown
Mozilla/5.0 (Windows NT.6.2; Win64; x64) Gecko/20011804 Firefox/21.0 Windows NT Unknown
Mozilla/5.0 (Windows NT.6.2; Win64; x64) Gecko/20011210 Firefox/21.0 Windows NT Unknown
Mozilla/5.0 (Windows NT 6.3; WOW64) Gecko/20142805 Firefox/21.0 Windows 8 Unknown
Mozilla/5.0 (Windows NT 6.3; Win64; x64) Gecko/20112003 Firefox/21.0 Windows 8 Unknown