Which part of the transaction does this occur at? Do you have a
specific URL? All of the VeriSign security seals are reporting
known and trusted host and the certs are matching.
They appear to be outsourcing their payment processing to
Convio. It's all matching up.
I clicked on the "Donate NOW" box on the front page, and it happened
during the redirect. I didn't get to see that they'd switched to
Convio at that point, because I wanted to keep the detail around, and
because hanging on that dialog suspends *all* of firefox's threads.
I finally released it, and I see that it's working OK now; I also see
that they switched that processing to Convio, and perhaps I got caught
in an out-of-phase moment.
I suppose I know better than to assume it's really broken until it
breaks three times in fifteen minutes (my own rule, ironically).