Due to a bug in Tor Browser , extra steps are required to use proxies with Tor Browser.
It would break Stream Isolation for Tor Browser as well as break Tor Browser's tab isolation by socks user name feature, thereby worsen your web fingerprint and be pseudonymous rather than anonymous. (To limit the risks, consider using More than one Tor Browser in Whonix or better Multiple Whonix-Workstations.)
1. Install FoxyProxy add-on in Tor Browser
2. Change Tor Browser Settings: