I'm having a weird problem where 4k videos that are scaled down to say the normal YouTube player size look terrible, hard to find the right word to explain it, but edges are jagged. It improves a lot if I full screen the player to presumably closer to 4k dimensions. Changing playback to 1080p looks better than 4k, again I'm sure it's to do with scaling. * I don't have this problem when testing the same videos in Internet Explorer. * It's not just my videos, other peoples videos are doing it to. * Updated to the latest version of Firefox. * Updated my GPU drivers (MSI Nvidia GeForce GTX 1660). * Tested in Firefox safe mode and disabled/enabled hardware acceleration. I'm running out of ideas, so any suggestions would be greatly appreciated.