There are methods for setting Tor Browser as your default browser, but those methods may not work always or in every operating system.
El Navegador Tor treballa fort per aïllar-se de la resta del sistema i els passos per fer-lo navegador predeterminat no són fiables.
This means sometimes a website would load in Tor Browser, and sometimes it would load in another browser. This type of behavior can be dangerous and break anonymity.