After much reading and interpreting, it became clear there was no more advice for configuration variations to get client cert login working. It seemed Chrome was doing it right, IE not even trying, and Firefox failing. No advice as to why and setting LogLevel to debug didn’t add much in the way of useful hints.
Jared Davenport, for reasons that would never have occurred to me, tried turning off TLS 1.0 in firefox as an allowed protocol. PCI compliance requires turning off a bunch of weaker/compromised protocols and ciphers anyway, so I already had:
SSLProtocol -ALL +SSLv3 +TLSv1
A quick test of
SSLProtocol -ALL +SSLv3
solved the problem with firefox. IE still refuses to talk to SSL, but IE is a stupidhead anyway. OK, it annoys me as the same client cert works on CACert.org’s site so something there is working right that isn’t on my box, but as I never use IE, I think I can let it go