$ python3 firefox_decrypt.py -vvv /home/user/tmp/back/.mozilla/firefox/
2020-01-06 12:05:29,866 - INFO - Running firefox_decrypt version: 0.7.0-76-g0996f45
2020-01-06 12:05:29,867 - DEBUG - Parsed commandline arguments: Namespace(choice=None, delimiter=';', export_pass=False, format='human', interactive=True, list=False, pass_cmd='pass', pass_compat='default', pass_prefix='web', profile='/home/user/tmp/back/.mozilla/firefox/', quotechar='"', tabular=False, verbose=3)
2020-01-06 12:05:29,867 - DEBUG - Running with encodings: USR: UTF-8, SYS: utf8, LIB: utf8
2020-01-06 12:05:29,867 - DEBUG - Skipping password store test, not exporting
2020-01-06 12:05:29,867 - DEBUG - Loading NSS library from libnss3.so
2020-01-06 12:05:29,868 - DEBUG - Loaded NSS library from libnss3.so
2020-01-06 12:05:29,868 - DEBUG - Reading profiles from /home/user/tmp/back/.mozilla/firefox/profiles.ini
2020-01-06 12:05:29,869 - DEBUG - Read profiles ['InstallCC254E9C9F4C4DA8', 'Profile1', 'Install21B45B3D0ECDD161', 'Profile0', 'General', 'Install8534878DEE63A580', 'Install9CA24498AC5F8684', 'Install4EBB9C042474750C']
Select the Firefox profile you wish to decrypt
1 -> idl912en.default-release-1
2 -> 6rlzgcf5.default-release
2
2020-01-06 12:05:35,847 - DEBUG - Profile selection matched 6rlzgcf5.default-release
2020-01-06 12:05:35,847 - DEBUG - Initializing NSS with profile path '/home/user/tmp/back/.mozilla/firefox/6rlzgcf5.default-release'
2020-01-06 12:05:35,850 - DEBUG - Initializing NSS returned 0
2020-01-06 12:05:35,850 - DEBUG - Retrieving internal key slot
2020-01-06 12:05:35,850 - DEBUG - Internal key slot <__main__.LP_PK11SlotInfo object at 0x7f64564b11e0>

Master Password for profile /home/user/tmp/back/.mozilla/firefox/6rlzgcf5.default-release:
2020-01-06 12:05:42,052 - WARNING - Attempting decryption with no Master Password
2020-01-06 12:05:42,053 - DEBUG - Database location: /home/user/tmp/back/.mozilla/firefox/6rlzgcf5.default-release/logins.json
2020-01-06 12:05:42,053 - INFO - Using /home/user/tmp/back/.mozilla/firefox/6rlzgcf5.default-release/logins.json for credentials.
2020-01-06 12:05:42,053 - INFO - Decrypting credentials
2020-01-06 12:05:42,053 - DEBUG - Reading password database in JSON format
2020-01-06 12:05:42,054 - DEBUG - Decrypting username data 'MEIEEPgAAAAAAAAAAAAAAAAAAAEwFAYIKoZIhvcNAwcECB6EeUto0kkiBBhgrv1t1ReC2KUBzLPTkQFfYEY9QcvbeIM='
2020-01-06 12:05:42,054 - DEBUG - Decryption of data returned -1
2020-01-06 12:05:42,054 - ERROR - Password decryption failed. Passwords protected by a Master Password!
2020-01-06 12:05:42,054 - DEBUG - Error during a call to NSS library, trying to obtain error info
2020-01-06 12:05:42,054 - DEBUG - PR_LOAD_LIBRARY_ERROR: Failure to load dynamic library