Fullscreen is disabled
https://support.google.com/youtube/answer/6276924
Fullscreen is disabled
If you have trouble using fullscreen on YouTube, here are some tips:
Check your browser's permissions
If the fullscreen button appears, but isn't responsive, you may have disabled fullscreen permissions for YouTube. Please check your browser's settings and permissions to make sure fullscreen is available on pages where you might use YouTube.
On Firefox, try the following steps:
1.In the location bar (where you enter URLs), type "about
ermissions" and hit enter.
2.Under "All sites", look at the permissions for sites you may have used fullscreen on, like youtube.com
3.You'll see a Fullscreen setting. Select "Always ask" or "Allow" to allow YouTube to go fullscreen on these sites.
4.Try using fullscreen on YouTube again.
On Chrome, you can set your browser permissions following the website permission instructions.
Check your browser add-ons and extensions
Certain browser add-ons and extensions may disable fullscreen mode. Please check your add-ons and extensions and change your settings as needed.
Other reasons why fullscreen is disabled
Fullscreen may also be disabled in the following cases:
•Your browser may not support fullscreen.
•The owner of the website who has embedded a YouTube player has disabled fullscreen.
