] Mouse movements in combination with a click-hold and
] optionally a modifier that execute some browser
] functions. You press mouse button, draw a gesture, and
] release mouse button (you can choose which button to use
] in advanced preferences). This gesture is recognized and
] appropriate action is triggered.

I know I am behind the times on this but if you are using mozilla without them, you are me three weeks ago. :) If you have a middle mouse button or your scroll wheel can click then these are definitely something you need to try. The tab navigation and forward / back movements are great. I can't see me going back to a browser without them ever again.

mozdev.org - optimoz: /gestures/index