@1. question: Yeah, currently it's limited to middle and left mousebutton only.
@2. question: It should be possible and due to high amount of user request it's planned for the next version (https://addons.mozilla.org/de/firefox/addon/gesturefy/reviews/931190/)

Edit: Right click is still working on Linux if you are using this trick: https://github.com/Robbendebiene/Gesturefy/issues/1 (just in case you aren't using firefox 57)