Command And Conquer: Tiberium Sun

Hint: Unlimited Firestorm Wall:
This trick allows a fully charged Firestorm Wall to last indefinitely without having to turn it off to recharge. First, fully charge your Firestorm Wall and turn it on. Before it turns off or runs out of power, sell or turn off your power plants until the message "On Hold" appears in the Firestorm Icon. Your Firestorm Wall will remain on indefinitely unless you build or turn on your power plants.

Hint: Firestorm defense:
Play as the GDI. If your enemy likes air units or missiles, surround your base with the Firestorm Wall at a distance from your base, backed up with RPG Launchers. Whenever aircraft or missiles are detected coming toward you, turn the Firestorm on. When aircraft attack, wait until just before they cross the Firestorm line so that they cannot turn away before they are hit. Do not worry if the Firestorm is attacked by the enemy aircraft -- it is pretty tough. Just bring some MRLS in to assist destroying the aircraft.