Youtube videos not showing properly

Hello,

Since about a week ago, my youtube on Firefox (doesn't do this on other browsers) started to show videos, that I start in a new tab in weird format (doesn't do this when I click it to play in the same window). The video has black space under the controls for the video, it sometimes has a little white dot next to the time and when I try to go fullscreen it leaves a lot of black space under the video and sometimes even on the sides and the fullscreen gets stuck and can only be stoped by pressing escape button. And when I press "i" for the mini player and then again to go normal size it fixes this. Except for Grammarly, I don't use any add-ons or motives.