I used to use this extension a long time ago. Unfortunately it looks like the website has been abandoned and left to rot. The © says 2021, but I suspect that's an automatically updated line. It feels like it's been updated since the last time I used it, but who knows how long ago that actually was.

The website is slow and sometimes crashes and times out. That's server side. Not Firefox. Small styles install, but if they're any more complex than a site skin, it takes too long to install and the longer it takes the more chance the site will crash before it's through.

I wish someone would take this whole thing and fork it into something someone has more passion for than the original authors do. Or let Mozilla Foundation bake it into Firefox.