The same thing every other sane gesture extension does. A. Use normal gestures. Right click and mouse drag right-left depending. Also, for back, 90% of users have a back button on mouse. And also, 90% times people use back instead of forward while browsing. So I'd say, making life easier to navigate between tabs is much more essential than going back or forward, since you are already able to do that.
Suggestions and feature requests
