Latest Iceweasel 6 user agents:

User Agent Platform Device
Mozilla/5.0 (X11; Linux x86_64; rv:6.0) Gecko/20100101 Firefox/6.0 Iceweasel/6.0 GNU/Linux Unknown
Mozilla/5.0 (X11; Linux i686 on x86_64; rv:6.0.2) Gecko/20100101 Firefox/6.0.2 Iceweasel/6.0.2 GNU/Linux Unknown
Mozilla/5.0 (X11; Linux i686; rv:6.0a2) Gecko/20110615 Firefox/6.0a2 Iceweasel/6.0a2 GNU/Linux Unknown