Ubuntu – How to connect to SFTP in FileZilla using a private key

I think what you're really looking for is keychain, which is similar to the ssh-reagent you mention. Once configured in your .bashrc it'll prompt for the passphrase of the key(s) you asked it to manage only when you launch the first terminal after login and makes sure every new terminal knows about your ssh-agent.

Sorry, the previously mentioned is not true. I was too naive that things can work out together.

In FileZilla you have to add the key using, menu Edit → Preferences → SFTP, as you did. Or make sure the key is in your ssh-agent before starting FileZilla (ssh-add -l should list the key).

You account in Site Manager has to have the "Normal" logon type with an empty password and the key should be tried automatically.