Picture-in-picture in the browser is a feature to let the user watch a video pop-out of a current tab and float it on top of other windows. This feature's been available in Google Chrome and Opera, just recently, Mozilla has brought it as a built-in feature for Windows with version 71 and macOS and Linux with version 72.
For Chrome users, picture-in-picture has been available as a built-in feature since version 70. Actually, you can enable this feature in two simple options, either use this built-in feature or install the Chrome extension.
If you use the extension, it’s an easier method even downloading the extension is an extra step. This extension adds a dedicated button next to the address bar that lets you reach it instantly by clicking on the icon to open a video in a picture-in-picture mode with a mini-player. You can also use the keyboard to enable as well by just pressing “Alt + P” on Windows or “Options key + P” on Mac.
Another option is using its built-in feature and it requires you to manually do a right-click on videos, but you have to do two times continuously to get the mouse menu pop-out.
Firstly, just make sure whether you have a Firefox version 71 for Windows and 72 for macOS and Linux but if not, you have to update your Firefox browser. Once your browser gets updated, you will see a small blue “Picture in picture” when you hover your mouse over it while the video starts playing on a page. Then it's really easy, you just click the button and the video will swap to picture-in-picture mode.
In default, picture-in-picture is enabled and you can turn it off or on by clicking "Enable picture-in-picture video controls" in its setting.
Among these three browsers, Opera may be the first browser to let you play a video in picture-in-picture mode. You can enable this feature by going to Opera setting and you will see "Video pop-out". You can toggle it on or off, but it's enabled by default.
Opera's video pop-out feature is super easy to enable. The video will soon pop-out over windows when you click on the "Clone" icon located on the top of the video.