Been using this script/addon since it was called YouTube + and tried many others like it like YouTube Center and various other userscripts. This one is unobtrusive, does what it needs to efficiently and gets out the way. Great way to set default video quality, video size, works with YouTube's dark theme, set your YouTube homepage to some other page (I choose subscriptions page), reverse video playlist order, disable comments if you want, and a floating video player as you scroll down the page, among many other features!! The only thing missing that Youtube+ had that Iridium doesn't have yet is being able to resize the floating video player when you scroll down pages. Please add that!