It doesn't work with Firefox 52 ESR (I'm stuck with Windows Vista at work, so I'm stuck with Firefox ESR, until it finally dies).

Working alternatives: FireGestures (legacy) and Foxy Gesture (only older versions still work on ESR, newer versions only work with newer versions of Firefox, the "Quantum" series). It would be nice to have more alternatives (mainly one that could be used both at work and at home, where I have an up-to-date system).

After developer reply: thanks for answering, raised one star for that! Unfortunately, just tried version 2.4 and it didn't work on Firefox 52.9.0 ESR...