The suggested fix for Tor and Firefox: “If you’re a Firefox user and would like Firefox to always render IDNs as their punycode equivalent when displayed in the browser address bar, type ‘about:config’ without the quotes into a Firefox address bar. Then in the ‘search:’ box type ‘punycode,’ and you should see one or two options there. The one you want is called ‘network.IDN_show_punycode.’ By default, it is set to ‘false’; double-clicking that entry should change that setting to ‘true.'”
The same fix worked for Palemoon, which I’m using right now.