YouTube full screen not working in safari

Go to Safari menu (At the very top right side of your screen next to Apple icon), choose "Quit Safari"

press "Shift" button and while holding this button on your keyboard single click on the Safari icon on your Dock.

Open Safari - Preferences - Privacy - Remove All Website Data.

Open the Go menu with Option (Alt) key pressed - Library - locate Safari folder and move it to your desktop.

I always forget to explain everything to the very end 🙂

No, it is safe to remove this folder as after you restart and open Safari, a new folder is created.

Same problem here on two MacBooks, a new MacBook Pro 13 and a new MacBook 12.

YouTube videos either blank on full screen (with sound) or white with a black box.

Moving the mouse restores normal fullscreen function but only for a few seconds.

Tried the above fix with no improvement. Also uninstalled Adobe Flash and re-installed.

Also have the problem with Netflix in fullscreen. Only with Safari.

Send Apple feedback. They won't answer, but at least will know there is a problem. If enough people send feedback, it may get the problem solved sooner.

Feedback

Or you can use your Apple ID to register with this site and go the Apple BugReporter. Supposedly you will get an answer if you submit feedback.

Feedback via Apple Developer

I seem to have solved it (we will see for how long). I logged into the other user account on my macBook and reset Safari there. Not sure if that makes any sense with the way different user accounts work. Could the cache on one effect the operation of Safari on another account? Or possibly this was just a fluke temporary solution.

I finally found the actual solution. None of the other common answers worked for me, like removing all website data, reinstalling flash, deleting the Safari folder in Library, etc.

The actual solution is as follows:

- Go to System Preferences > General

- Under the "Show Scroll Bars" section, check either "Automatically based on mouse or trackpad" or "When scrolling."

Voila! Problem solved. The problem occurs when "Always" is checked. I guess YouTube doesn't play well with that option.

Thank you blendedreality!

it was really helping me.

at last, i can sleep.

I have a fix, without any updates! - Go to System Preferences > General - Under the "Show Scroll Bars" section, check either "Automatically based on mouse or trackpad" or "When scrolling." The problem is often, when the option "Automatically based on mouse or trackpad" is checked!