History touchscreen gestures por Maurizio Macrì

Apparently, Firefox doesn't have touchscreen gestures to navigate browsing history, so this is an attempt to bring the feature in. One finger swipe left to navigate back, one finger swipe right to navigate forward, as simple as that. Bear in mind it doesn't work on native firefox pages (about:home, about:config, etc), and on the Firefox addons site (https://addons.mozilla.org).