OK I'll give have a shot at summing up:
Opera declares itself as Opera, or Opera Mini for the mobile version. No lizard mentioned.
We are not concerned with strings containing Mozilla unless they also contain Gecko.
Safari (desktop or mobile) and Konqueror say they are also KHTML (like Gecko).
Chrome, Android and Omniweb say they are also KHTML (like Gecko) and Safari.
iCab for OSX says it is also KHTML (like Gecko). The OS9 version is simply iCab.
NetFront is a mobile browser occasionally containing "like Gecko".
Firebird and Phoenix are old versions of Firefox, and all three admit to being Gecko.
Firefox says it is Firefox except when it is Deerpark, Minefield, Granparadiso or BonEcho (often a Yahoo bot).
Flock and Camino say they are Gecko and also contain Firefox in their string.
Seamonkey, Netscape, Epiphany, K-Meleon, Galeon, Iceweasel, Iceape, Webzebu, Thunderbird, Chimera, Amethyst, Ideal Browser, Sylera, ACommunicator, Amico Alpha, Foxybird, Kazehakase, Beonex, Skipstone, Songbird, Swiftweasel and OpenVMS all identify themselves and mention Gecko.
Anything else containing "Gecko/" and a version less than or equal to 1.7.13 is probably plain Mozilla.
Except that Mnenhy and (in some cases) Firesomething may be mentioned, indicating possible tampering.
And there could still be some exotic and obscure reptiles lurking in the undergrowth.
And anyone can change their user-agent easily, be they human or robot.
And the IP was from Websense, so UA was definitely spoofed anyway.