The channels are not individually controlled so it shouldn't if you have issues with stereo you can employ mono.

Unless it's in the exclusion list, it shouldn't display this message. Please paste your log in the github issues..... you can also temporarily downgrade to an older edition from the github releases page or the versions page on mozilla https://addons.mozilla.org/en-US/firefox/addon/volume-control-boost-volume/versions/
Hope I can help you resolve your problem and you can revise your review to 5 stars. I jut do this as a hobby.

Its because steam blocks it in their CSP, sadly lots of CDNs do.
I could individually add each one to the FQDNS list, but like you said that's a lot of hassle and it has to be reaproved by mozzila everytime etc.
The way audio source is pulled is on page load. If it's doing it too late lots of sites won't interact with the plugin. Where as its an issue on sites with strict CSP as then it just blocks audio.
So sadly there's nothing I can do about it, without further reducing compatible sites.
Could maybe make a whitelist mode instead of a blacklist mode in the future.

I hope you revise your review as it "works good"

It's most likely because it interacts on page load and your site has a strict CSP. If you add it to the FQDNS list the page may then work.

Sadly, I was having a lot of issues implementing the ability to save the volume per page, and most videos on a page are diferent volume anyways so this is not a planned feature.

That shouldn't be possible its initialized per tab.

It works but some sites have CSP rules that block it from initializing/breaks audio. Add those sites to the blocklist in the settings.

It works but some sites have CSP rules that block it from initializing/breaks audio. Add those sites to the blocklist in the settings.