YouTube is testing an image-in-picture function for desktop computers, as reported by 9to5Google. For those who have it, the test will mimic what is already available on YouTube for Android and iOS, allowing users to minimize and watch a video while continuing to browse.
If available in your account, you can play a video and then click anywhere on YouTube to navigate without the video disappearing. Instead, the video will be minimized as a floating window in the lower right corner of the screen and the video / audio will continue to play. The controls will continue to be available in the floating video, including playback / pause, replay and the ability to see the next clip. The name of the video will still appear below, and a small icon in the lower right corner allows you to access full playlists. 9to5Google says you do not see a way to turn off this test feature if your account has one; You must manually close the video.
It is not clear if YouTube will implement this in all accounts, if it will be restricted as a function for YouTube Red accounts, or really, if it will be widely implemented. It is a useful feature already on Android and iOS devices, and with a YouTube music streaming service on the horizon, it would be an excellent way to make navigation songs on the platform a more fluid experience.