> When you turn on the computer firefox works well, then you suspend and when
> you return from suspend firefox has the above mentioned symptoms. Is this
> correct?
Yes. The exact details are inthe bug report I linked earlier so I won't repeat them here.

> It could help if you would describe your configuration (hardware: board
> video card). I remember you mentioned somewhere else HDMI.
I've experienced this on several different machines and what they all have in common are nvidia's 
proprietary drivers. These are known to do a poor job with resuming from suspend. I just tested 
how Chromium video playback behaves after waking from suspend and it has a similar problem. The 
difference is that with Chromium only rendering of the page is broken and refreshing it fixes the 
problem. With Firefox the whole browser window disappears and there's no way to restore it.

> Another question: Do you know what is the difference between X11 and Wayland?
My layman's understanding is that Wayland replaces X11 but it's not a drop-in replacement and 
requires that a window manager implements support for it. And I understand XWayland acts as a X11 
compatibility layer on top of Wayland. That's basically my whole knowledge of Wayland.

Janek