Optimoz (http://optimoz.mozdev.org/) is a project that is working on mouse gesture (mozgest) and pie menu (radialcontext) support for Mozilla web browser platform.

I personally consider both of these things (well, pie menus at least) very important for improving user interface because they're better than "normal" menus in many ways. It is also good that they don't entirely replace them, so there's no compatibility issues either. Both work nicely alongside normal Mozilla controls - for example, you can still use mouse drags however you want, and gestures work when they have to; If there's something that's in context menu but not in radial menu, Ctrl+right click will bring forth the normal context menu.

From what I have seen, RadialContext is working pretty well, and it definitely helps an instant Neverwinter Nights (and I believe also The Sims) addict to experience the web the nice and easy way. While I haven't personally used the gesture module that much, former Opera fanatics say it's working pretty well.