1) Go to C:\ProgramData\Xfire and double click xfire_games.ini Note: Program Data folder is hidden.
2) Scroll down to [5993] LongName=Call of Duty: Modern Warfare 2 Multiplayer and under it, replace with LauncherExe=LaunchIW4M.exe and with DetectExe=iw4m.exe and save it.
3) Now got to Xfire and click Tools and Options, you'll be able to see Games menu ..and under it there are Installed Games and Not Installed, double click Not Installed and scroll down until you see Call of Duty: Modern Warfare 2 Multiplayer.
4) There is Automatically Detect which you have to click to Manual Detect and under Game Path: browse to C:\Users\***\AppData\Local\IW4M\LaunchIW4M.exe..Note: *** is the admin user. For Detect Path, set path to your Game Folder for iw4m.exe and click OK under it.
5) That's it..just restart your xfire. Hope it works for you all.