Samizdata - 8:02 pm on Nov 9, 2008 (gmt 0)

I don't have a comprehensive answer but testing for the presence of "Gecko/" (with the slash) and
then the absence of Firefox or Netscape should narrow the field down quite a lot.

The slash is important to exclude browsers (Chrome, Safari, Camino) that use "like Gecko" in the UA string.

The old Mozilla browsers are no longer supported and must be pretty rare. Here's one:

Mozilla/5.0 (Macintosh; U; PPC Mac OS X Mach-O; en-US; rv:1.7.13) Gecko/20060414

...