Security warning first: this copy of Volume & Sound Booster contains malware
Do not install this XPI. If it's installed in any of your browsers, remove it.

The real volume feature is the ~150 lines in cs.js. The other files (csvolume*.js, amplify-relay-bg.js) are pieces of unrelated libraries (Dark Reader, AdGuard scriptlets, lodash, Vue) with renamed functions. That filler hides a remote-control loader:

Delayed start: amplify-relay-bg.js:770-790 saves an install timestamp and does nothing for about 3 days (laneGapMs = 258200000). This is a common way to get past store review.
Hidden server address: csvolumepatch.js:808-812 calls cloudflare.com/cdn-cgi/trace to get a value h. That value is part of the key that decrypts the server URL, so the URL can't be read from the code alone.
Network rules from the server: amplify-relay-bg.js:825-840 downloads a payload and applies it with declarativeNetRequest.updateDynamicRules. That lets the server redirect requests or rewrite headers on any site.
Remote code in every page: csvolumepatch.js:850-890 runs code from that payload inside each page, using new Function(body)() or a function exported into the page via wrappedJSObject. It skips pages that contain a certain "guard" string.

Doesn't even install the right extension, this and the other volume control extension both add the exact same extension that is a different one. I don't know what this is but it feels weird because it doesn't give me what it should give me

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Disables sound completely if I change volume.

Does not work

It doesn't do anything. is it an scam?

Garbage does not work.

Like others have noted. Doesn't do anything.

just straight up doesn't do anything

I don't know what's going on, but it no longer looks anything like the images and doesn't work at all.