I asked your question on the tor-talk mailing list and got the following reply from one of the creators of Tor itself:
You should really avoid making exceptions to the proxy rules for Tor
Browser. If you let your browser connect to local services, that opens
the door for remote websites, which you access over Tor, to give you
make local connections and then send that info back to the website.
In the most benign case, you're setting yourself up with a tracking
marker ("there's that weird person who allowed connections to
192.168.1.1 again"). In worse cases, you're opening yourself up to permissions surprises and attacks that start with the word
"cross-site" or "cross-protocol".
For an early example of a similar bug that bit Tor users, see
All of that said, if you still want to shoot your feet off: in
about:config, there's a network.proxy.no_proxies_on option that you
For even more details, new in ESR68, there is now a
network.proxy.allow_hijacking_localhost option, which we needed to fix
for Tor Browser: https://bugs.torproject.org/31065
So, with that answer, a best practice would be to use a standalone browser instance for local network access.