FireGestures is a great little free add-on for the Firefox Web browser that allows you to perform many different actions, such as going back to the last page or opening a new tab, with your mouse and a quick flick of the wrist.
You typically use FireGestures by holding the right mouse button and moving the mouse in one or more directions--up, down, left or right. The add-on comes pre-configured to assign gestures for many tasks, such as left for going back in the history, or up-down to reload the page. You can quickly re-assign a gesture or assign a gesture to a new task using the FireGestures options.
To help you along, FireGestures can trace a colored line as you move the mouse (after holding the right button) so that you can tell what kind of gesture you're making. You can also choose to bring your mousewheel into the mix for some gestures.
FireGestures is one of my must-have add-ons for Firefox. Sure, much of what it does also has an associated key combo (such as Ctrl-T for opening a new tab). But use it, and you'll quickly see how much more convenient it is to use your mouse.