The short version, if you arrived here from a search: Your automation browser may not run cross-document view transitions at all. Check that before you debug anything else. If you replace the default transition animation, you inherit mix-blend-mode: plus-lighter , which was chosen for the animation you just deleted. That is your brightness pulse. A hard white blink before the transition is not the transition. It is an unstyled frame of the incoming document painting the UA default. ...