Thank you for the positive feedback! That is a great idea. I am gonna try to add such a page in the feature.

Update 07. June '18: As you said it was pretty easy to change the addon. In the latest version 1.2.3 you can customize the gestures. The settings page can be openend with the guesture Down-Right-Up-Left or when you open 'about:addons' and then select 'Mobile Gestures'. There you can use D for Down, U for Up, R for Right and L for Left. Right now there is no input checking. But this will be added as well.