On an OS X desktop with Firefox I don't see the behaviour you describe, no. I am able to view the video full screen fine.
This thread title has "mobile"—and indeed there I have problems on iOS 8.
It's basically a bug and one that's been around for a while. I don't know how high it is on the developer's list of things to do. The temporary fix I suggest is to switch it off and use right sidebars, but I realise that it's not ideal.