I've been using Greasemonkey for so long, it has become a habit in time. Never looked for anything else as it did what I wanted without any hassle.

Then comes Firefox Quantum. And for some reason, Greasemonkey decided to throw away backwards compatibility, which ended up more than half of my scripts not working anymore. On top of that, it lost its usability, by showing every single script, having no options menu of any kind, a script editor that cannot even rival Notepad (yes, the default Notepad the Windows has), and so on.

So I looked for an alternative, and realized that Tampermonkey is not just a Chrome add-on, there also exists a Firefox Quantum compatible version. Switched over, copied my scripts, and everything is working properly. Then discovered the rest of it; excellent UI, lots of options, great editor, and many more.

I don't think I'll be going back, and had I knew the quality work that has been put into Tampermonkey, I'd have switched before. Never looked for anything else Greasemonkey, but I'm really glad it gave me a reason to look for something else with its Firefox Quantum update, as it led me to discover Tampermonkey, and as I've said, I wish I had looked into this long before.