works only on a fresh page since some youtube update in their codes. The script does not work in playlist. "DownloadYoutubeAsMP4" has added a line in its script for his to work. If only I could find which line, I would add it to yours and tell you if it works.
I hope you can work this out and make an update.
edit; ok now the script load, but the toolbar-playlist-toggle-buton is nowhere to be found :-(
your last 2 updates have not resolve this yet again....
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