Chromium 51 shows a grey line at the under the fullscreen video with RASPBBIAN 8

[Matteo Raggi]

With Raspbian 8, raspberry pi 3 model B, Chromium 51 I see a grey line (it is 10-11 pixels high and it is long for all the browser width) at the bottom of fullscreen video (both with etensions and without extensions). On the same raspberry and raspbian withfirefox 45.5 the video is perfect, but strongly teasing (Screen tearing) the image slides are mroe teasing too. 
With the same video it doesn't happen with android 5.1.1 on zidoo x5 and with windows 10 64 bit and chrome 55 64 bit,

instead it is perfectly fullscreen on the same hdmi tv 1920x1080 pixel.
my config.txt customization is very simple for now:
framebuffer_width=1920
framebuffer_height=1080 
Here the example of what I see, both fullscreen and not.

Any ideas?