[shock]

On Linux I use the EasyGestures application which I've configured to send XF86Back and XF86Forward keys for the respective gestures. The added benefit is that the back and forward gestures work in the other apps too, not just in Firefox.

[ConfucianNardin]

For anyone else looking, the parent probably meant 'easystroke': https://github.com/thjaeger/easystroke

It's likely available from your package manager.

[shock]

Indeed, I did. Thank you for linking to it, I was in a hurry when I posted.