I used Greasemonkey 3 for Firefox 56.0.2 for ages, and I really, really loved it! But I'm switching from Firefox 56.0.2 to 66.0.5 now, and Greasemonkey 3 no longer exists. Now there is Greasemonkey 4. I will quickly tell you three big flaws with Greasemonky 4. 1.) It no longer supports stuff like GM_addStyle, so a lot of your previous user scripts will break and stop working. 2.) Greasemonkey 4 doesn't even have word wrap on the script editor page. I kid you not. You have to continuously scroll back and forth to the right back to the left back to the right, again and again, just to see your code. and 3.) Greasemonkey 4 doesn't even have a dedicated page that lists all of your user scripts. It does include some or all of those user scripts in the popup menu that displays when you click the browser extension button, but they should have a dedicated page for all user scripts that you have installed. So I tried TamperMonkey which had the things I wanted, but the UI is ugly and some of the stuff like word wrap was buried deep and hard to find. Also, I think that word wrap in a script editor should be on by default. So then I gave VioletMonkey a try, and even though it isn't 100% perfect (it almost is), it is by far much better than Greasemonkey 4 or TamperMonkey. It supports GM_addStyle, it has a beautiful interface, easy-to-read script editor with word wrap on by default, and much more. It's also open source. I never bothered trying to edit open source stuff before, but maybe I will customize this VioletMonkey one day and make my own Monkey that has a few UI improvements. I highly, highly recommend VioletMonkey. It might be new, it might not have many users, and maybe some idiots will try to scare you away from it. But it is far better than any competition and deserves to be referred to as the #1, best userscript manager out there.