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I wanted to like FireMonkey, but unfortunately it seems to be incompatible with the vast majority of scripts I use with the Waze Map Editor downloaded from greasyfork.org. There are no JavaScript errors -- the scripts just do nothing. They are listed as active on the page, but something about them just doesn't work with this addon. So I'll have to switch to a different one.

The UI is much better and more intuitive than that of TemperMonkey.

I really like the distinction between CSS and JS modifications and that I don’t need to use “proprietary” GreaseMonkey functions like GM_addStyle (` /* the CSS goes here */ `).

FireMonkey also doesn’t exhibit the bug that TemperMonkey does — when I navigated the same portal over many pages, it seemed TM kept adding the same CSS script over and over, which, over time, slowed Firefox noticeably (after a while TM reported aplying about 70 scripts instead of 2!).

Seems like we can't import scripts from zip
Right, unzip everything and import works, but slightly inconvenient, thank you for replying.

Perfect better than the alternatives.

It is indeed super lightweight. A nice advantage to being on Firefox, as it's not available elsewhere.