Slow game in full screen

Hi I'm doing a 1280x720 resolution platformer, but I noticed that it works fine only when the browser is halved, if I try to play in full screen it slows down a lot, this even if I only keep the main character with few animations without enemies and background. Why does this happen?

I reactivated the hardware acceleration, I restarted the chrome and now it is a splinter, I hope it will be useful to someone, thanks anyway to those who have read!