Can you connect to the server with same settings using another tool (like FileZilla)?
Did you make sure the connection is not blocked by your firewall?
I use Fireftp extension in Waterfox which is very easy and allows viewing the html page live in the browser. In Fireftp, the moment I select SFTP it asks fo a private key which I'm not sure where to get it from(the server uses Direct admin and allow the creation of a public key in SSH section, I "guess" it's there that the key is generated). There's no instructions on using SFTP both in the Direct Admin help section and on the internet/youtube and this is frustrating.
In WWB publish settings I don't find any place that asks for a key private or public.
The firewall is not blocking the ftp connection as I can easily publish WWB using normal FTP.
I can continue to use the normal FTP connection but if SFTP is available which is more secure, then I'm trying to use it.
From reading that you are using fireftp perhaps the following may be of help (or not). Although it talks about Firefox and links to Waterfox as a alternative it does explain the use of a "Private Key" ,where to find and how to use. http://fireftp.net/help.html (Read from Account Manager->Private Key)