Wenn du den Tor Browser und einen anderen Browser zur selben Zeit laufen lässt, gefährdet dies weder die Leistung, noch die Privatsphäreeinstellungen von Tor.
However, be aware that when using Tor and another browser at the same time, your Tor activity could be linked to your non-Tor (real) IP from the other browser, simply by moving your mouse from one browser into the other.
Or you may simply forget and accidentally use that non-private browser to do something that you intended to do in Tor Browser instead.