macbook pro with retina display video playback slowdown ?

my 15 inch macbook pro with retina display has been working perfectly fine but whenever i'm watching youtube videos in full screen (it also occurs on other sites) there is a very noticeable frame drop, almost like its playing at like 18 frames per second (just a random number), when its just in the browser window and not full sreened it's fine smooth playback

and even if it's a 480p video it does the same in full screen and when its 1080p and not in fullscreen it doesn't do this

i've had this laptop for 2 months now and this just started happening recently and it is very very annoying, especially since i'm always on youtube and i also make videos myself, i don't mean to sound harsh but i didn't spend almost 3 grand for a laptop to find several flaws in it over time.

if there is a fix for this or even any suggestions i'd be grateful for any help!