GREAT

Since a couple versions ago the addon lag out the browser to the point of unusability. Had to disable it. In the good days it was great.

Installing immediately tanked performance of Youtube to the point where I was only able to watch a single short before everything stopped working.

Used to be good in the past. Now not so much. While there are a lot of great options i consider a must have, sadly it makes youtube tabs extremely heavy and also near unusable. The YT interface becomes laggy and tabs freeze constantly.
Worse is that it happens on both Chrome and Firefox on two different PC's. (even worse is that performance issues have been present for a long time now, they just got worse and worse over time with each update)

Since the last update, i can't even open the settings anymore, it just says "asking your browser what settings you made here before" (on the FF PC) so i can't even export my settings (or more importantly, the watched list) anymore.

Sadly all of that means that the addon is unusable and simply does not work as intended anymore.
I hope it will improve at some point, but for now i can do nothing but to remove the addon for good, from all my devices.

I added that extension, set some basic functions in first category and YT page couldn't load with Firefox popup that extension slowing down browser.. uninstalled.

The settings will not be retained. Every new page load is unchanged even though the settings are listed as active.

While the features this addon provides are great, I am unable to use any of them because every time I attempt to install this extension, my computer becomes unusably laggy regardless of whether youtube is active or not. My computer gets so laggy that youtube videos are no longer able to play. Am not sure if this is an issue on my end or on the developer's end but this extension is completely unusable for me.

For the past few days, some YouTube pages in Firefox have been experiencing terrible page freezes. The built-in manager shows a load of 100% or even 200+%. When the add-on is disabled and the page is reopened, everything returns to normal.

The fit-to-window feature is mostly what I wanted, and it works properly. I wanted it to hide the recommendations column completely as I find those distracting, while having the video as large as possible without fullscreening the browser.

Better settings than youtube themselves. Obviously.

Worked well until it started crashing both my Zen browser and my wife's Waterfox with memory exhaustion.

It has stopped autoplaying next short, very irritating