where to set socks proxy server (address/port) in thunderbird

[Skaperen]

i need to use a socks proxy server (SOCKS5 as supported via ssh) to access my IMAP/SMTP server from here (where only destination ports 80 and 443 can make connections).
but the latest Thunderbird does not make it easy to find where this is.
note that i currently have NO accounts set up in Thunderbird.
help i found so far says to set this in the account info.
but setting up an account FAILs because it cannot connect to the mail server yet.
i need to get the account setup logic to do its connection test via the socks proxy.
FYI: firefox is connected through this socks proxy right now. i am doing this post via it.
FYI2: this socks proxy is running via ssh that connects via port 443 to an outsider server configure for sshd to listen on port 443 on a spare IP address.
the big question thus is: how to configure Thunderbird to use a socks proxy in general for everything before any accounts are set up so it does account tests via the socks proxy.

edit:

when i configure thunderbird like i configure firefox ... for sock proxy ... it still tries to make connects direct (e.g not using socks) for the account setup tests