You do not. Tor browser is just a browser and proxy baked together for convenience. You can use any proxy and any browser you want.
Actually, tor is also not browser centric at all either. It does TCP (if not more), so any protocol will do. Proxy is typically a SOCKS interface IIRC, so any client will often do as well.
Yeah, that’s not practical, if you can’t access a certain tld without using a special network, then you lost the purpose of having it in the first place. onion needs tor network, browser or not, plus the horrendous name too. A practical convenient tld is where you use any browser on any internet connected device to type a human readable name.