luis_v replied at 2015-4-9 04:50
As A.S. said, it's only available on Flash videos, and because Youtube is moving away from flash to HTML5 your only option is to use an extension to force Flash to work.
Either use the one linked above, or Youtube Centre, which offers more options for customising Youtube, including downloading videos.
There was talk of implementing a popup feature for HTML5, but it's unknown if or when that might happen.