Config_mouse allows one to change the context the mouse; say for example if it has two button instead of three (so the user doesn't have to set the 2-Button Viewing Mode).
If you have a 2-Button mouse and don't want to have to set it every time, add the following line to your pymolrc file.
config_mouse two_button # put the mouse in the cool-new movie-enabling mode config_mouse three_button_motions
Three-Button Motions Mode
The Three_Button_Motions mouse configuration mode has been added to PyMOL. To use it, first prepare the mouse mode:
# put the mouse in the cool-new movie-enabling mode config_mouse three_button_motions
and then click on the mouse-panel (lower right hand side of PyMOL window) until you see a boxed "M" appear in the openGL menu window above. (It should appear after the "C" for Color).