For me, I think the Chrome version actually did work for a while, but it stopped working some months ago, and has not worked since. Unfortunately, I don't recall what version of the browser or the extension made the difference, but as an avid user of both, I would very much appreciate some eyes on this.
As reported above, the symptom is that the player becomes completely unreponsive. This issue does not occur in Chrome-based browsers.
As for the Firefox version, it seems to have been removed from addons.mozilla.org, but is still available via https://www.mrfdev.com/enhancer-for-youtube. In any case, it still has no effect, and is probably not worth trying to make work anymore.
