Using !Tor without #TorBrowser makes you vulnerable to DNS request leaks, and other nasties. I've seen this using #Thunderbird, which is just awful (ie. leaky) for all sorts of things (POP3, SMTP, IMAP, extensions). Not all data for every layer escapes, but there's enough leakage that anonymity is compromised. #TorBirdy is a Thunderbird plugin to reduce that kind of leakage. See https://trac.torproject.org/projects/tor/wiki/torbirdy TorBrowser has added !security hardening to !Firefox to minimize vulnerabilities; if you're going to the trouble of using Tor you may as well use TorBrowser since that's no extra effort.