Expand Audience with Third "Popup Option"
Hello - I believe the audience of your extension could be expanded if you added one feature to your "options" menu. You currently have two options under your "Popup options" section. I'd like to propose a third: "Allow Controlling Extension from Popup* Options", which would be enabled by default, and have all the same behavior of the extension in its current form.
If you disable this option, then the Music Mode On/Off switch and the Current Tab On/Off switch would disappear from the Popup Options menu. This would mean that the extension is always forced to be on while it is enabled.
The audience this would appeal to would be people interested in purposefully restricting themselves from visual youtube content, but wanting to allow audio youtube content. There would easily be a handful of users of an internet filter software "Plucky" (https://pluckyfilter.com/) who would begin using your extension every day, and suggest to others that they do the same. Plucky (and likely other self control softwares) can restrict disabling extensions and changing extension settings from the Chrome extensions page (chrome-extension://abbpaepbpakcpipajigmlpnhlnbennna/pages/options.html), but do not allow for restricting changing settings from the Popup Options menu. As of today, then, this extension is not useful for self-restricting users because they can simply disable it from the Popup Options menu, but with this extra option, this demographic could have access to all youtube audio content while being unable to access youtube visual content, which would be instrumental for this demographic. To my knowledge, there is no other extension that has this functionality.
I, for one, would certainly begin using it each and every day, and would donate to support your development.