User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/109.0

Steps to reproduce:

• I configured an X.509 key pair to be used for a specific account, the same one to be used for signing as well as for encryption.
• I did NOT have a GPG key for this account.
• I kept the default of "Disable encryption for new messages" selected, and
• I checked "Sign unencrypted messages".
• I deselected "Store draft messages in encrypted format" (shouldn't matter for this issue, but I'm mentioning it anyway).
• I was unable to select from the button cluster "Preferred encryption technology" because this button cluster seems to be disabled if you only have one technology configured.
• I composed a message to myself and tried to send it.

Actual results:

I got an error message saying "Cannot digitally sign this message, because you haven’t yet configured end-to-end encryption for <target-addr>".

Obviously this is because the default of "OpenPGP" in the compose window was selected. Once I changed this to S/MIME, I was successfully able to send the message, and it was indeed signed using S/MIME (no other tech was available anyway for this account).

Expected results:

S/MIME should have been selected automatically as the default encryption technology, because that is the only one available/configured for this account.