fix(python): fingerprint_preset=False no longer turns presets on

launch_options checked `fingerprint_preset is not None`, so passing False
drew a random bundled preset, the opposite of what was asked. It now uses a
truthiness check, and a test proves that None and False never draw a preset.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

pythonlib/camoufox/utils.py

@@ -1038,7 +1038,7 @@ def launch_options(
         # User passed a custom fingerprint
         if not i_know_what_im_doing:
             check_custom_fingerprint(fingerprint)
-    elif fingerprint_preset is not None:
+    elif fingerprint_preset:
         # User opted into real fingerprint presets
         if isinstance(fingerprint_preset, dict):
             preset = fingerprint_preset

pythonlib/tests/test_identity_salt.py

@@ -162,3 +162,11 @@ class TestPrefsEnvIsAscii:
         joined = "".join(env[f"CAMOU_PREFS_{i}"] for i in range(1, len(env) + 1))
         assert joined.isascii()
         assert orjson.loads(joined) == prefs
+
+
+@pytest.mark.parametrize("off", [None, False])
+def test_fingerprint_preset_off_never_draws_a_preset(off):
+    """`fingerprint_preset=False` means off, the same as None. It used to be
+    checked with `is not None`, so False drew a random bundled preset."""
+    with mock.patch.object(utils, "get_random_preset", side_effect=AssertionError("preset drawn")):
+        launch(fingerprint_preset=off)