Mozilla/5.0 (Windows NT 6.1; WOW64; rv:12.0) Gecko/20120428 Thunderbird/12.0.1
Just to complete this discussion for the sake of the archives, the
crashes I was getting resulted from a Cygwin bug, which has been fixed
in the 2012-05-25 Cygwin snapshot. But I still think that the patch I
applied makes sense, as long as it doesn't cause other problems down the
road.