Unirgy DropshipSplit

Open app/code/local/TM/FireCheckout/Model/Quote/Address.php and find following line:

class TM_FireCheckout_Model_Quote_Address extends Mage_Sales_Model_Quote_Address

Replace it with:

class TM_FireCheckout_Model_Quote_Address extends Unirgy_DropshipSplit_Model_Quote_Address
// Mage_Sales_Model_Quote_Address

Save the file and disable compilation mode, if needed.