Finally a gesture add-on that works well on FF 57! Well done
The settings UI could use some work. For examnple, on the tab where you choose the gestures to control the actions, you have to hover to see the gesture. It would be much better if all the gestures were displayed, so you could see which gestures were being used and for what. Hovering just adds needless steps that make it tedious to configure. And that's true for quite a fgew other things, where you've gone for clever, but pointless UI tricks, like animation etc, but not focussed on making it simple and easy to use.