Move an off screen window back on screen¶

For some reason, sometimes when I double click on Title Bar, the window shrinks to zero and it's impossible to resize again.

Solution:

1. Swipe up with three fingers (Mission Control)
2. Select the window
3. Click on the Window menu, then click Zoom

Source: https://superuser.com/questions/55341/move-an-off-screen-window-back-on-screen-on-mac-os-x