How to make in X11 so that the focused window follows the mouse?

Another long title.

Just a quick one, not to forget: in Apple’s X11, if you want to have the focus follow the current window, just type the following at the terminal window:

defaults write com.apple.x11 wm_ffm -bool true

Restart X11 and that’s it! This is particularly useful in apps like Gimpshop that have several open windows simultaneously (for the palettes, the layers, and the images themselves).