use-dialog-box

use-dialog-box is a variable defined in `C source code'.
Its value is

t

Documentation:
Non-nil means mouse commands use dialog boxes to ask questions.
This applies to `y-or-n-p' and `yes-or-no-p' questions asked by commands
invoked by mouse clicks and mouse menu items.

On some platforms, file selection dialogs are also enabled if this is
non-nil.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 21.1 of Emacs.