If you want to use OutWit Hub or any or our programs with the Tor browser, you can simply browse to outwit.com with Tor, click on the download link and select the Firefox add-on version in the version menu (bottom item). That’s it.
[Update] Tor 6.0 is now based on Firefox 45. Which means that it has the same signature restrictions and cannot run OutWit extensions. At this point, the only solution is to use Tor Browser 5.5.5.