Engine Editor takes advantage of extra buttons in your mouse, having a 5/6-button mouse will give you the best experience with the Editor.

Logitech G502 HERO Mouse
Across the Editor there are following shortcuts defined for the mouse buttons:
Rotate Camera is assigned to 2 buttons, Middle - for those that don't have extra buttons, Fourth - for those that have extra buttons since they're more comfortable than the middle-click which is usually used for the mouse wheel.