The fullscreen button received an update so when you are viewing a YouTube video, you will have the option to shrink, expand, or view the video in fullscreen. Additionally, recommended video content will pop out when clicked so you can easily exit to where you last were before clicking after viewing.
Google has yet to make an official statement about any of the changes. The search giant has been working to integrate its social platform Google+ into each of its products. Currently only a small group of users have access to the redesign, so don’t be disappointed if you don’t see it.