RE: 2004 Volvo S60 - Fuel Filter
Greetings from Yokohama.
As I'm not privy to S60, I am not sure exactly where the FF is located and believe those in the S60 section will be able to assist you. In the case of 850, it is on pax-side, right by the rear wheel.
In case if the quick disconnect is stubborn, try twisting the fuel lines while pulling on them. Also, make sure to relieve the fuel system pressure before proceeding, I'm sure you know it.