To use pop-up menus in the Source Browser dialog box, position your
  mouse pointer in the dialog box, and press MB3.  A pop-up menu with the
  following items appears:

  Expand                 Expand the selected image or module to include its
                         component modules or functions in the Source
                         Browser display.

  Collapse               Collapse an expanded image, module, or function display.

  Display Source         Display (in the source display of the source view
                         on the main window) the source code associated
                         with the selected module.

  Set Breakpoint         Set a breakpoint on the selected function.

  Step                   Step to next line, stepping over routine calls.

  Go                     Resume execution of program.