Great, but... Rated 4 out of 5 stars
It's great for flash player YouTube, doesn't work for html5 though.
It allows to set many things making YouTube more convenient to use.
Unfortunately it has some bugs.
First it sometimes doesn't start buffering right away and I have to manually start it.
Second is that sometimes doesn't load properly. Pop-up window shows only one line with donation and global settings and auto-pause doesn't work then.
They're annoying, so I hope it will be fixed.
One more thing. I don't know what's a desktop notification, but why can't you give an option to use a build-in notification in Firefox?