When playing YouTube videos in fullscreen mode, the video appears to skip as would be expected with frame drops. However, with stats for nerds open on the videos, no frame drops are reported and buffer health is fine (40+ seconds).

I'm on an up to date version of FireFox, I've tried with hardware acceleration both enabled and disabled, I've tried opening task manager to see if system usage looked weird (it doesn't, although it's not like I can have TM running while the video is playing in fullscreen so hard to tell) and am at a complete loss. All drivers for CPU and GPU are verifiably up to date (did full system check three days ago) and the only conclusion I've been able to come to is that it must be either a problem with FireFox or a problem with YouTube. I've seen no recent reports on any of the forums that I can find pointing to either as the culprit. So if anyone has any further ideas or solutions, I'd love to here them.