Sorry for the bad formatting, apparently I cannot edit my comment on HN anymore.
1. Go to System Settings -> Keyboard -> Keyboard Shortcuts -> App Shortcuts
2. Click the small (+) button under the shortcuts table
3. Choose/Type the following values in the modal:
- Application: All Applications
- Menu Title: Zoom
- Keyboard shortcut: Command + Shift + M (My preferred shortcut)
4. Click Save.
5. Voila, now you are able to maximize any window, and pressing it again it goes back to its original size. A cool trick is that now if you hover the green (+) button on the top of any page you will be able to access that shortcut from there as well. It sits just under the "Enter Full Screen" menu option.
