I think that a break statement should do the trick... So:
Code:
for (var i:Number = 0; i < Main.floors.length; i++)
{
	if (Main.floors[i].hitTestObject(this))
	{
		grav = 0;
		jumped = false;
                break;   //////////THIS LINE
	}
	else
	{
		grav++;
	}
}
Hope that works...