By default, the Maximize (green) button on iTunes places the application in mini player mode instead of maximizing the application. Instead, you have to press the Option button on the keyboard while clicking the Maximize button to achieve a maximized window. This tech-recipe will show you how to reverse this where Maximize is the default setting for the button.
1. Close iTunes.
2. Open Terminal.
3. Execute the following command:
defaults write com.apple.iTunes zoom-to-window -bool YES
4. Open iTunes and the Maximize button works like it should.
To reverse this, close iTunes, open Terminal and execute the following command:
defaults write com.apple.iTunes zoom-to-window -bool NO