When you don't have a middle button, mouse chording (left+right at the same time) is usually configured to simulate the middle button (for instance, the Emulate

When you don't have a middle button, mouse chording (left+right at the same time) is usually configured to simulate the middle button (for instance, the Emulate3Buttons option in the classic X server configuration). Once you get used to it, it's nearly as convenient as clicking a physical middle mouse button.