Both. I use it with waterfox/firefox but I see it’s available for Chromium based browsers, Chrome, Brave, Edge. Yes, MS Edge is now Chromium based.
https://duckduckgo.com/?q=Enhancer+for+Youtube&ia=web
I saw the listing in the Chrome webstore, but there are some comments there that are unsettling. Some say it works, others say it don’t. Not sure what to believe.
Well, Youtube is finding a way around Enhancer now as well. I got it installed, and it worked for a few days, but I’m getting that popup again. Have you had any problems as of late?