Pre - Install the Patch (Select your "Counter Strike Source" Folder properly)
1. Install X-Fire
2. It will automatically Detect most installed games
3. If CSS is not detected, Go to Tools > Options > Games double click on NOT-INSTALLED, from the games list
Thats it !
If you did not make any mistakes, it should work out fine, and your XFire profile will be updated soon. It is not instant.
Let me know if you face problems.
Credits - Patch created by FTI from DigitalZone
[ Official Release Thread ]