In brief: Avid users of YouTube's mobile app have probably taken advantage of its "Miniplayer" feature on several occasions. The Miniplayer will automatically pop out the video you were watching while you visit other channels or in-app menus. Now, that feature is available for desktop users as well - but in the form of a dedicated button toggle.
YouTube's desktop version is pretty solid as is, but it's been inferior to its mobile counterparts in one area for some time now - the Miniplayer. If you don't tend to use YouTube on your smartphone, the Miniplayer is, as the name suggests, a miniature video player that follows you throughout the platform.
If you begin looking for another video to watch, the video you were watching will be minimized into one corner of your screen, allowing you to pause, play, maximize or close it at will. It's a pretty handy feature to have at your disposal, and it's recently arrived for desktop users, too.
The Miniplayer button can be seen towards the bottom-right corner of the video playback area.
Avid YouTube users may already have noticed this feature, but for those who only watch YouTube occasionally, accessing the Miniplayer is easy: just open up a video of your choice, and hit the small double-rectangle "Miniplayer" button located towards the bottom-right corner of the video playback area. The video will then pop out and, as previously mentioned, continue to play as you browse the site.
The Miniplayer is a fairly addition; a quality-of-life change at best. However, it's nice to see that Google isn't abandoning its desktop users despite its focus on the YouTube mobile app's various incarnations.