SYMPTOMS:
Make sure your monitor supports the resolution you chose.  Setting a  
resolution higher than what your monitor supports in windowed mode  
can create an issue where you may not be able to access the "apply"  
or "revert" button because the window will appear larger than your  
monitor's native resolution and these options will appear off screen.

RESOLUTION:
If you have encountered this issue you will need to delete the  
etqwconfig.cfg file in your "Home / Library / Application Support /  
ETQW / Base folder".  Doing so will change your settings back to  
default the next time you launch the game.