Decrypt every saved login in a Firefox profile directory (needs both key4.db and logins.json).
Tips & Tricks
A Firefox profile directory is usually named something like xxxxxxxx.default-release under AppData\Roaming\Mozilla\Firefox\Profiles\ (Windows) or ~/.mozilla/firefox/ (Linux) — grab the whole folder (e.g. Compress-Archive/zip), not just key4.db, since logins.json holds the actual encrypted credentials.
If the profile has a master password set, firepwd.py will prompt for it — without it, decryption fails even with both files present.