If you're using one of my public proxy servers, you can ignore this message.
But if you're self-hosting an fTelnetProxy installation, then you'll need to download the latest binaries from GitHub to fix a TLS issue. Firefox 74 has disabled TLS 1.0 and 1.1 by default, so this new fTelnetProxy release enables TLS 1.2 support to ensure Firefox users can still connect.
Unfortunately this required upgrading to the .NET framework version 4.5, which means if you don't already have that version of the framework installed you'll have to install it first.
Which also unfortunately means XP is no longer supported, because as far as I know XP does not have an install for .NET 4.5. So if you're using XP either stick to the old version and turn off https when serving the fTelnet client, or switch from self-hosted to one of my public proxies.