Liferea right now doesn't support SOCKS proxies. In Debian bug #272178 David Smith hints on how to workaround this. Full quote:
Just some information for people wanting to use Liferea with SOCKS. I'd strongly recommend that you install the package redsocks. I've found that this works perfectly, not only for liferea, but for *ALL* other applications whether they support SOCKS or not, to tunnel all their traffic through a SOCKS (or SSH Tunnel) server. It is no longer necessary, today, to build SOCKS support into every network application, even if you *MUST* use SOCKS. For this reason, it's unlikely liferea will ever get SOCKS support. There's just no reason for it. I've just completed testing of liferea + redsocks through a SOCK5 connection created inside an SSH tunnel and it works just fine. I used the guide available here: http://dtbaker.com.au/random-bits/redirect-all-traffic-through-transparent-socks5-proxy-in-linux.html Thanks for your time.