This page let you install a bookmarklet to see the main video (the first one with max heigh on the current page) on the current page with the new mode "Picture on picture" (See the can-i-use reference about picture in picture).

To install the bookmarklet : Drag'n'drop the link : PiP into the bookmarks bar of your browser.

To use the bookmarklet : On a page with a video, just click on the "PiP" link and the video will appear in PiP mode.

Github project : https://github.com/gissehel/pip/