YouTube video dont change smoothly to fullscreen in Firefox

[PunGun]

Hello, when i open Firefox 55.02 (64bit) normaly without Sandboxie and change a YouTube Video to fullscreen there is a smoothly transition.
But in Firefox running with Sandboxie it change not smoothly, same when i close the fullscreen mode.

When you change the transition duration in about:config from "200 200" to "0 0" on following commands(in Firefox not running with Sandboxie) you can see how it looks like when i enter or leave the fullscreen mode in a YouTube video in my sandboxed Firefox:

full-screen-api.transition-duration.enter
full-screen-api.transition-duration.leave

Windows 10 Home (64 Bit)
Sandboxie 5.20 (64 Bit)
Firefox 55.02 (64 Bit)
Windows Defender

I know its not a big Problem but i think to fix it wouldn take a long time.

[Barb@Invincea]

Hello PunGun,

I tested the scenario and noticed the difference that you are referring to.

The devs stated they will keep an eye on this, but they are not looking at working on a direct fix right now. Maybe a future update will take care of it.

We will update this thread if new information becomes available.

Regards,
Barb.-