Mozilla Adding a Picture-in-Picture Mode to Firefox
Like Chrome, Mozilla Firefox is adding a Picture-in-Picture Mode that allows users to pop the video out of the web page in a stay on top frame that they can watch while using other applications.
In a recently updated Mozilla bug post, the Picture-in-Picture feature has been enabled in the Firefox Nightly build. Using this build, you can go to a YouTube video and right-click on it twice to show a menu that contains a "Picture in Picture" option.