firefox and https

[Patrick Welche <prlw1%cam.ac.uk@localhost>]

Just trying the shiny new firefox 57.0, I get

   Error code: NS_ERROR_NET_INADEQUATE_SECURITY

for as far as I can tell, every https page (eg duckduckgo, bbc.co.uk).
I tried importing a couple of certs from /etc/openssl/certs, but
the interface told me they were already installed. Clearly lots
changed since 56.0.2...

Cheers,

Patrick