Hi Eran,
Yes you can do that in
Source, Add -> Browser Source -> Copy the URL address of the Video in YouTube and paste it the Browser Source, remove the CSS, the Width and Height is up to you then hit Ok.
After that, right click the BrowserSource that you created, click Interact then click the full screen in youtube video, you can even change the resolution settings. (recommended to make it HD)
You can do that multiple times.
In facebook, almost the same approach, instead of copying the whole address of the video in facebook, just need to type the URL address of facebook (
www.facebook.com) then login with your account, the find the video, hit full screen. Of course you need to make this BrowserSource as Interact first before you can type anything/login.