What are mouse gestures?
A mouse gesture is a way of combining computer mouse movements and clicks which the software recognizes as a specific command.
Why are they useful?
Gestures help you avoid moving your hands back and forth from the mouse to the keyboard. This speeds up web browsing, thus increasing productivity. It also helps you avoid having to aim for small buttons (like back, or refresh) when using an application.
In Firefox, holding ctrl (Apple key on Mac) and scrolling the mouse-wheel up or down changes the text size.
If you enable right-click-and-drag gestures with a Firefox extension, you can go back a page by holding the right mouse button and dragging your mouse to the left. Similarly, you can go forward by dragging right. The different extensions have different default gestures and levels of configurability. Other popular gesture actions for browsers include common tasks such as creating new tabs, closing tabs, moving up in the directory structure, or incrementing a number in the URL.