I was putting up with choppy videos for a while on fullcreen Youtube 720p60 1080p60 videos in Firefox.
I have 2 x 4k, 28" Screens.
This also worked for 2160p 4k Youtube content
Today I found the solution:
1. Put
about:config into Firefox's address bar and hit enter.
2. Search for
layers.acceleration.force-enabled3. When this value comes up, double click the word
false under the value column to change it to
true4. Restart Firefox.
FYI, in Chrome I experienced no such issues.
Hurrah, no more chop!