fix(python): give NewContext identities the browser's Firefox version

NewContext() and AsyncNewContext() passed ff_version=None through to
generate_context_fingerprint(), so a context's user agent kept the version
fpgen drew (e.g. Firefox/146) while the browser underneath was 152. They
now default ff_version to the major version of Playwright's
Browser.version, which Juggler reports from MOZ_APP_VERSION_DISPLAY, so the
UA always names the browser the page is actually talking to. An explicit
ff_version still wins.

The docstrings said each context gets "its own real fingerprint preset";
the default has been an fpgen draw, with a preset only when one is passed.

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

docs/per-context-patches.md

@@ -610,7 +610,7 @@ bundles are shipped in the wheel.
 
 | Property | Source | Notes |
 |----------|--------|-------|
-| UA, platform, HWC, oscpu | fpgen or preset | UA version patched to match Camoufox Firefox version |
+| UA, platform, HWC, oscpu | fpgen or preset | UA version patched to the browser's Firefox version (NewContext reads it from Playwright's `browser.version` unless `ff_version` is given) |
 | Screen dims, colorDepth | fpgen or preset | Viewport adjusted by -28px for browser chrome |
 | WebGL vendor/renderer | `sample_webgl()` from `webgl_data.db` | OS-weighted probability sampling. fpgen's own WebGL fields are not mapped in `fpgen.yml` yet, so both paths call `sample_webgl()`. |
 | Font list | `_generate_random_font_subset()` | One weighted OS-version base in full, plus each addition unit at its measured probability; marker fonts always included. See [FONTS.md](FONTS.md). NOT from presets. |

pythonlib/camoufox/async_api.py

@@ -195,15 +195,15 @@ async def AsyncNewContext(
     """
     Creates a new browser context with a unique fingerprint identity.
 
-    Each context gets its own real fingerprint preset (navigator, screen, WebGL, fonts, etc.)
-    with its own audio noise seed. All values are applied
+    Each context gets its own identity (navigator, screen, WebGL, fonts, voices),
+    drawn by fpgen unless a preset is given, with its own audio noise seed. All values are applied
     via addInitScript so they self-destruct before page scripts can detect them.
 
     Parameters:
         browser: A Browser instance from AsyncNewBrowser or AsyncCamoufox.
-        preset: A specific fingerprint preset dict to use. If None, picks randomly.
-        os: Target OS for preset selection ("windows", "macos", "linux").
-        ff_version: Firefox version string for UA patching.
+        preset: A fingerprint preset dict to use. If None, fpgen draws a new identity.
+        os: Target OS for the drawn identity ("windows", "macos", "linux").
+        ff_version: Firefox major version to claim in the UA. Defaults to the browser's own.
         webrtc_ip: IPv4 address to spoof for WebRTC ICE candidates.
         proxy: Per-context proxy (Playwright format: {"server": "...", "username": "...", "password": "..."}).
             Unless webrtc_ip and timezone_id are both given, they are looked up from the
@@ -211,6 +211,10 @@ async def AsyncNewContext(
         geolocation: Per-context geolocation ({"latitude": float, "longitude": float}).
         **context_kwargs: Additional Playwright new_context() options.
     """
+    # The drawn UA carries fpgen's Firefox version, which must not disagree with
+    # the browser the page is actually talking to.
+    ff_version = ff_version or browser.version.split('.', 1)[0]
+
     # Auto-derive WebRTC IP and timezone from proxy's exit IP when not explicitly provided
     if proxy and (not webrtc_ip or "timezone_id" not in context_kwargs):
         exit_ip, timezone = await _resolve_proxy_geo(proxy)

pythonlib/camoufox/sync_api.py

@@ -173,15 +173,15 @@ def NewContext(
     """
     Creates a new browser context with a unique fingerprint identity.
 
-    Each context gets its own real fingerprint preset
-    with its own audio noise seed. All values are applied
+    Each context gets its own identity (navigator, screen, WebGL, fonts, voices),
+    drawn by fpgen unless a preset is given, with its own audio noise seed. All values are applied
     via addInitScript so they self-destruct before page scripts can detect them.
 
     Parameters:
         browser: A Browser instance from NewBrowser or Camoufox.
-        preset: A specific fingerprint preset dict to use. If None, picks randomly.
-        os: Target OS for preset selection ("windows", "macos", "linux").
-        ff_version: Firefox version string for UA patching.
+        preset: A fingerprint preset dict to use. If None, fpgen draws a new identity.
+        os: Target OS for the drawn identity ("windows", "macos", "linux").
+        ff_version: Firefox major version to claim in the UA. Defaults to the browser's own.
         webrtc_ip: IPv4 address to spoof for WebRTC ICE candidates.
         proxy: Per-context proxy (Playwright format: {"server": "...", "username": "...", "password": "..."}).
             Unless webrtc_ip and timezone_id are both given, they are looked up from the
@@ -189,6 +189,10 @@ def NewContext(
         geolocation: Per-context geolocation ({"latitude": float, "longitude": float}).
         **context_kwargs: Additional Playwright new_context() options.
     """
+    # The drawn UA carries fpgen's Firefox version, which must not disagree with
+    # the browser the page is actually talking to.
+    ff_version = ff_version or browser.version.split('.', 1)[0]
+
     # Auto-derive WebRTC IP and timezone from proxy's exit IP when not explicitly provided
     if proxy and (not webrtc_ip or "timezone_id" not in context_kwargs):
         exit_ip, timezone = _resolve_proxy_geo(proxy)

pythonlib/tests/test_new_context_version.py

@@ -0,0 +1,36 @@
+"""A context's user agent carries the Firefox version of the browser it runs in.
+
+Without an explicit ff_version, NewContext kept whatever version fpgen drew
+(e.g. Firefox/146) on a 160 browser, so the UA disagreed with every
+version-dependent API the page could probe.
+"""
+
+import asyncio
+import re
+from unittest import mock
+
+import pytest
+
+from camoufox import async_api, sync_api
+
+
+def _user_agent(init_script):
+    return re.search(r'setNavigatorUserAgent\("([^"]+)"\)', init_script).group(1)
+
+
+@pytest.mark.parametrize("api", ["sync", "async"])
+def test_user_agent_matches_the_browser_version(api):
+    context = mock.MagicMock()
+    browser = mock.MagicMock()
+    # Playwright's Browser.version for Firefox: MOZ_APP_VERSION_DISPLAY.
+    browser.version = "160.0.1"
+    if api == "sync":
+        browser.new_context.return_value = context
+        sync_api.NewContext(browser, os="linux")
+    else:
+        context.add_init_script = mock.AsyncMock()
+        browser.new_context = mock.AsyncMock(return_value=context)
+        asyncio.run(async_api.AsyncNewContext(browser, os="linux"))
+
+    user_agent = _user_agent(context.add_init_script.call_args.args[0])
+    assert "Firefox/160.0" in user_agent and "rv:160.0" in user_agent, user_agent

pythonlib/tests/test_proxy_geo.py

@@ -34,6 +34,7 @@ EXIT = {"status": "success", "query": "203.0.113.7", "timezone": "Europe/Paris"}
 
 def _sync_browser():
     browser = mock.MagicMock()
+    browser.version = "152.0.4"
     return browser
 
 
@@ -41,6 +42,7 @@ def _async_browser():
     context = mock.MagicMock()
     context.add_init_script = mock.AsyncMock()
     browser = mock.MagicMock()
+    browser.version = "152.0.4"
     browser.new_context = mock.AsyncMock(return_value=context)
     return browser