Just use this javascript in brownser console (open with F12 and choose console). You can replace this 2.75 in the end with what you want. I use it to watch 3h of lecture in one hour because estonians simply talk slowly 🙂
document.querySelectorAll('video').forEach(v => v.playbackRate = 2.75)
For convenient use you can save it as a bookmark and it should change the speed of the video:
javascript:document.querySelectorAll('video').forEach(v => v.playbackRate = 2.75)