The typical path is: [Game Root]\zone\english\ for English versions. Example: C:\Program Files (x86)\Steam\steamapps\common\Call of Duty Modern Warfare 2\zone\english\
If you own a legitimate copy of Call of Duty: Modern Warfare 2 on Steam, follow these steps: zone code-pre-gfx-mp.ff download
The internet is filled with shady "file download" websites offering standalone .ff files. We strongly advise against downloading single DLL or FF files from unknown sources. These are often vectors for malware, keyloggers, or corrupted data. The typical path is: [Game Root]\zone\english\ for English