1px white border visible on fullscreen video playback

To reproduce, play a video fullscreen. Note the 1px white border on the sides and bottom of the screen.

This doesn't occur in Firefox, so I'm not sure if there's an additional fingerprinting concern here too (i.e. from TB users' fullscreen resolutions being slightly different from FF users for the same devices, although I see bug 1450401 is still open anyway).