You can create a bookmark containing JavaScript code which opens a popup. The steps to do this are detailed in Nonny Moose's answer. However, in order to make the bookmark work in all cases, including videos you are watching as part of a playlist or which were linked to at a specific timestamp, the following code is more robust:
javascript:window.open("https://www.youtube.com/embed/"+window.location.toString().match(/\?v=.{11}/)[0].substring(3), "_blank", "left=0,top=0");
Optionally, add window.history.back();
to the end in order to make the original page stop playing and go to the previous page. This solution still does not work with videos set to disable embedding.
In order to set the popup to always be on top, you can use the following AutoHotKey script (assuming your laptop's operating system is Windows):
#NoEnv ; Recommended for performance and compatibility with future AutoHotkey releases.
; #Warn ; Enable warnings to assist with detecting common errors.
SendMode Input ; Recommended for new scripts due to its superior speed and reliability.
SetWorkingDir %A_ScriptDir% ; Ensures a consistent starting directory.
!^+A:: Winset, Alwaysontop, , A
This allows you to toggle whether the current window is set to be always on top by pressing Ctrl+Alt+Shift+A. For information on how to use AutoHotKey, use the Online Documentation. In particular, replace !^+A
with another code as detailed here to change the hotkey.