How to fix YouTube fullscreen not working problem during playing videos on browsers, Chrome, Firefox etc.? Read this article to get troubleshooting tips.
1. Update Browser & Flash Player to Latest Version
No matter which browser you use right now, we suggest you to update it to the latest version with the support of HTML5 player to avoid fullscreen problem when playing HTML5 video on YouTube.
Apart from browsers, Flash Player may cause various YouTube playback problems as well. It's better to keep Flash Player for Chrome, Firefox and other browsers up-to-date.
2. Disable Browser Extension
Input "Chrome:extensions" on address bar for Chrome or "about:addons" for FireFox. Hit enter to get full lists of plug-ins. Uncheck "Enable" for Chrome or click "Disable" for Firefox to eliminate their interruptions on YouTube video fullscreen playback.
3. Download YouTube Videos
If you have tried the above two ways but YouTube fullscreen is still not working, we can suppose that fullscreen is disabled for a YouTube video (especially embedded ones on other sites) by owner. Therefore, the best way to make any YouTube video play in fullscreen is to download YouTube videos to computer or devices and use a video player to reach fullscreen playback.