Installed the extention, it worked for a first 3 times then extention's blue button near a notification bell disappeared to never be seen again when I was in the middle of rearranging my playlists. So its useless right now. Thankfully I've got backup of my playlists but the damage has been done.

Edit: now the button appeared, but I can't import videos from an exported backup list I've done in the previous version, no matter whether its JSON or TXT format. Pasting copied videos from extention memory does not seem to work either. On all my efforts it responds with only "precondition check failed" error message.

UPD: It appears that Precondition check fail error was due to playlist having removed/private videos, so selecting these videos for copying or moving into another playlist results in failure. Other than that extention works fine.