Useful add-on with loads of powerful features, love the ad-blocker, and the default quality setter, in fact, just about every feature and option you can think of ever needing, including the ability to add some custom Javascript so you can add that essential missing feature (you know, the one that would get them into trouble if they added it, but it would 'save' you a lot of fiddling about if they were allowed to add it).

I wish it also worked on other video sites, but it's still more than you should expect for nice software that the developer has put a lot of time and thought into crafting, and is offering you for free.

If you view YouTube a lot, this extension is absolutely essential. You would need several other YT extensions added together to do what just this one does - and I haven't noticed it slowing down my browser, either.