SOCKS5 (Tor) is not honored in plugins
"Plugin installer", "HttpUpload", "Url image preview", and possibly all others do not work with Tor SOCKS proxy, even if it is set as global proxy in Settings. I can see from iptables logs that it tries to connect directly.
I found this closed issue #45 (closed). But the problem is that Tor is SOCKS proxy, not an HTTP proxy, so it won't work.