Wow, Opera has a built-in video pop-out feature. That's very nice. I wrote a script to do that in X11 a while ago: https://github.com/myfreeweb/dotfiles/blob/32c9cfd8d5e0a3a2c... after I saw a Mac app that does this.
Being its own app you can of course have this window floating and on top of your firefox window off in the corner. You could even designate a hotkey to move and resize this window to that position if you so desired.
https://chrome.google.com/webstore/detail/fulltube/nmabgnejf...
source code: https://github.com/ijanos/fulltube
I tested Opera's video pop-out as an alternative to macOS's PiP. What is positive here is that Opera's mode supports most of the video players. Also what I like in Opera's mode is that you can actually control the timeline in the pop-out which seems useful.
But the deal-breaker is when you change focus between desktops (Apple's Spaces). Opera's video pop-out doesn't follow you. Actually you have to transfer the browser window with you on the other desktop in order to have the video pop-out which kinda brakes the point of the feature for me.
[0] - https://www.igeeksblog.com/how-to-enable-picture-in-picture-...
First you add custom URI in windows, lets call it magnet3 (this should be a clue, it works just like torrent magnet links):
[HKEY_CURRENT_USER\SOFTWARE\Classes\Magnet3]
@="Magnet URI"
"URL Protocol"=""
"Content Type"="application/x-magnet"
[HKEY_CURRENT_USER\SOFTWARE\Classes\Magnet3\shell]
@="open"
[HKEY_CURRENT_USER\SOFTWARE\Classes\Magnet3\shell\open]
[HKEY_CURRENT_USER\SOFTWARE\Classes\Magnet3\shell\open\command]
@="\"C:\\Users\\me\\Documents\\js\\youtube-dl mplayer.bat\" \"%1\""
set var=%1
for /f "delims=" %%A in ('d:\_learning\youtube-dl.exe -f best -g "%var:~9%') do start "" "C:\Program Files\smplayer\smplayer" "%%A"
set var=%1
start "" "C:\Program Files\smplayer\smplayer" "%var:~9%
Rube Goldberg sequence of hacks, but works perfectly.