It's disturbing that you use original developer's nickname.

I've been using Video Speed Controller and it makes adjusting playback speed on any HTML5 video effortless. The fine-grained control and keyboard shortcuts are very convenient for lectures and tutorials. It remembers settings per site and feels lightweight, reliable, and smooth without interfering with normal viewing experience at all sessions.

Do not install this extension! This is not the original Igrigorik author! See their GitHub for confirmation.

One-starring to spread awareness that both the extension and the author of this Firefox port has no ties to the original project, as by Igrigorik's disclaimer on their Github issues page. Avoid installing/enabling since this is very suspicious behavior.

Sketchy af. The original author disavow this add-on. github.com/igrigorik/videospeed/issues/1511

works