Nah, I did the following:
I picked a video in my Youtube app that I know has 60fps options. Then I switched to Firefox, played the same video and checked the quality options.
In the app, it gives you the options 720p60, 1080p60 for example. In firefox, it does not.
60 FPS videos are only available at 720p and above, so maybe your browser is defaulting to 480p?
Nah, I did the following: I picked a video in my Youtube app that I know has 60fps options. Then I switched to Firefox, played the same video and checked the quality options. In the app, it gives you the options 720p60, 1080p60 for example. In firefox, it does not.
Does it work for you in Firefox mobile?