Mozilla has been working on the implementation of Picture-in-Picture (PiP) mode for web videos in Firefox Nightly Builds, and the feature is now available in the browser's Beta and Developer Edition channels. Even in its experimental stages, the function is being tested by the developers, who are said to be still "accentuating the accessibility of the keyboard, as well as some problems on how the video is shown in extreme window sizes" .
In case you still do not know, the Picture-in-Picture mode allows users to see a video as a pop-up window that is always up and can be moved or resized as needed. It also allows users to quickly play or pause the video by hovering over it with the mouse, which exposes a control panel with options to play, pause, close and more.
While the feature was originally scheduled to debut with Firefox 68, Mozilla developers Mike Conley and Andreas Bovens say the organization is trying to get more feedback from users before releasing them to the stable channel. According to them, the developers have devised two ways to display a video in an Image in Image window, one of which is through the contextual menu in a video element, as in the screenshot below.
The contextual menu option, however, does not work on many sites, including YouTube, which replaces the default context menu with yours, which is why Firefox developers include a picture-in-picture switch (the blue element in the screenshot below) "that slides out when you hover your cursor over it." Clicking on the blue rectangle opens the underlying video in image-in-picture mode. According to Mozilla, the switch can work in most of the sites outside the box without requiring any additional work by the authors of the site.
So, if you want to try the new feature, you can do it by downloading Firefox 69 Beta.