I wish Shadertoy had an easier way to let me change framerate. If you click 480Hz on a 120Hz display, it flickers at an awful 15Hz instead of 60Hz; so you don't want to simulate a 15Hz CRT -- not comfortable.

Retroarch now has this CRT simulator and it will automatically keep it at 60Hz by its default settings; so it's more foolproof in Retroarch than in Shadertoy.