abcjs player mod per DaveRo

THIS ADDON NO LONGER WORKS IN editor.drawthedots.com
Due to some changes in abcjs it no longer mutes voices which is its main purpose. It does still suppress chords and repeats. It may work again if I can find an alternative way of muting voices: https://github.com/paulrosen/abcjs/issues/945
It does still work in Michael Eskin's player which uses as modified abcjs.
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Adds buttons to https://editor.drawthedots.com/ to add playback options.
Suppress guitar chords, individual voices, and repeats. Each of these can be turned on or off.

It also works on http://michaeleskin.com/abc

After loading a new tune you may have to press the 'Reset' button to detect the number of voices, if that has changed.

Settings permissions
This addon is MV3. You need to manually grant permission to access the website(s), either on initial installation or when you first access each site. If you don't, the buttons will not display. You can also remove permission from either site if it stops working correctly - e.g. after an update to that site.

Android - as at June 2024.
MV3 extensions are only now being implemented on Android.
Firefox versions up to 126: Does not work. Permissions are not implemented.
Firefox version 127: Mostly works. You can grant permission to both sites on installation, but you cannot see or amend permissions in the Extensions Manager.
Firefox version 128: Fully works. You can grant permissions to both sites on installation and you can see and remove permission for either site in the Extensions Manager.