You are right. There are options to enable/disable SSLv2 and SSLv3 but not TLS. I just filed an RFE: http://bugzilla.mozilla.org/show_bug.cgi?id=208193.
So, the only way to disable TLS right now is to disable
all the TLS cipher suites individually.
That doesn't work. It is not the case tht the ciphersuites whose names begin with SSL only work with SSL, and the ones whose names begin with TLS only work with TLS. All the TLS and SSL3 ciphersuites work with either/both TLS and SSL3. TLS and SSL3 differ in the way they handle things that are common to all ciphersuites, such as key derivation, and computation of the various MACs. The ciphersuite names differ acording to whether the ciphersuite was invented before or after RFC 2246 was published.
There's no substitute for being able to enable or disable TLS itself.
