fix(juggler): never enter Responsive Design Mode, and warn about is_mobile

#798 left RDM on for isMobile, as Playwright's Juggler does. RDM matches
no real browser: Firefox for Android never runs it, and under touch
emulation it drops a mouse click's pointer events, which no device does.
Camoufox only has desktop identities, so an is_mobile context was a
desktop UA, platform, fonts and GPU with devtools' mobile mode on top.

Juggler now keeps inRDMPane off for every page, is_mobile included, and
the isMobile plumbing #798 added is gone again. viewport-no-rdm requires
is_mobile=True to keep the platform's scrollbars too.

Both launchers warn instead (warnings.yml is_mobile): on new_page() /
new_context(is_mobile=True) of a Camoufox browser, and on is_mobile
passed to launch_options() for a persistent context. has_touch,
device_scale_factor and viewport keep working without RDM.

Upstream playwright-python skips its isMobile tests on Firefox in
1.61-1.63, so no skiplist entries are needed.

On beta.31 with this Juggler in omni.ja, viewport-no-rdm passes: 12/12 px
of scrollbar with no viewport, with a viewport, and with is_mobile, and a
has_touch click fires pointerdown and pointerup. pythonlib 411 passed;
typescript 584 passed.

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

pythonlib/camoufox/async_api.py

@@ -17,6 +17,7 @@ from .ip import Proxy, proxy_exit_geo
 from .utils import (
     async_attach_vd,
     attach_no_viewport_default,
+    attach_desktop_only_warning,
     attach_stock_media_defaults,
     launch_options,
     STOCK_MEDIA_DEFAULTS,
@@ -173,6 +174,7 @@ async def _launch(
     if no_viewport_default:
         attach_no_viewport_default(browser)
     attach_stock_media_defaults(browser)
+    attach_desktop_only_warning(browser)
     return await async_attach_vd(browser, virtual_display)
 
 

pythonlib/camoufox/sync_api.py

@@ -14,6 +14,7 @@ from .fingerprints import generate_context_fingerprint
 from .ip import Proxy, proxy_exit_geo
 from .utils import (
     attach_no_viewport_default,
+    attach_desktop_only_warning,
     attach_stock_media_defaults,
     launch_options,
     STOCK_MEDIA_DEFAULTS,
@@ -148,6 +149,7 @@ def NewBrowser(
         if no_viewport_default:
             attach_no_viewport_default(browser)
         attach_stock_media_defaults(browser)
+        attach_desktop_only_warning(browser)
         return sync_attach_vd(browser, virtual_display)
     finally:
         if pid:

pythonlib/camoufox/utils.py

@@ -683,6 +683,27 @@ def attach_stock_media_defaults(target: Any) -> Any:
     return target
 
 
+def attach_desktop_only_warning(target: Any) -> Any:
+    """Warn when new_page()/new_context() asks for is_mobile: Camoufox only has
+    desktop identities, and Juggler ignores the option (TargetRegistry.js)."""
+    for name in ('new_page', 'new_context'):
+        original = getattr(target, name, None)
+        if original is None:
+            continue
+
+        def wrap(original: Any) -> Any:
+            @wraps(original)
+            def wrapper(*args: Any, **kwargs: Any) -> Any:
+                if kwargs.get('is_mobile'):
+                    LeakWarning.warn('is_mobile')
+                return original(*args, **kwargs)
+
+            return wrapper
+
+        setattr(target, name, wrap(original))
+    return target
+
+
 def attach_no_viewport_default(target: Any) -> Any:
     """
     Default new_page()/new_context() to no_viewport=True.
@@ -1417,6 +1438,9 @@ def launch_options(
     if disable_coop:
         LeakWarning.warn('disable_coop', i_know_what_im_doing)
         firefox_user_prefs['browser.tabs.remote.useCrossOriginOpenerPolicy'] = False
+    # A persistent context takes its context options here.
+    if launch_options.get('is_mobile'):
+        LeakWarning.warn('is_mobile', i_know_what_im_doing)
 
     # Drop values the source supplied that this identity cannot keep, before the
     # WebGL pool below defers to them (a preset's own GPU pair wins over

pythonlib/camoufox/warnings.yml

@@ -41,6 +41,13 @@ instant_animations: >-
     never waits on one. A page can see it: getComputedTiming() reports a duration
     of 0 where stock Firefox reports the real one.
 
+is_mobile: >-
+    Camoufox is built for desktops and only draws desktop identities, so is_mobile
+    cannot produce a believable phone and will leak: the page still sees a desktop
+    User-Agent, platform, fonts, GPU and screen. Camoufox ignores is_mobile rather
+    than put the page in Responsive Design Mode, which a page can read too.
+    Use has_touch, device_scale_factor and viewport for the parts you need.
+
 block_webgl: >-
     Disabling WebGL is not recommended. Many WAFs will check if WebGL is enabled.
 

pythonlib/tests/test_identity_salt.py

@@ -191,3 +191,11 @@ def test_instant_animations_warn_that_they_are_detectable():
 
     with pytest.warns(LeakWarning, match="getComputedTiming"):
         launch(config={"instantAnimations": True}, i_know_what_im_doing=False)
+
+
+def test_is_mobile_warns_that_camoufox_is_desktop_only():
+    """A persistent context takes its context options at launch."""
+    from camoufox._warnings import LeakWarning
+
+    with pytest.warns(LeakWarning, match="built for desktops"):
+        launch(is_mobile=True, i_know_what_im_doing=False)

pythonlib/tests/test_launch_environment.py

@@ -388,3 +388,32 @@ class TestStockMediaDefaults:
         assert browser.kwargs["forced_colors"] == "active"
         # the ones the caller left alone still follow the host
         assert browser.kwargs["reduced_motion"] == "no-override"
+
+
+class TestDesktopOnlyWarning:
+    """Camoufox has only desktop identities and Juggler never enters Responsive
+    Design Mode, so is_mobile on new_page()/new_context() gets a LeakWarning."""
+
+    class FakeBrowser:
+        def new_page(self, **kwargs):
+            return kwargs
+
+        def new_context(self, **kwargs):
+            return kwargs
+
+    def test_is_mobile_warns(self):
+        from camoufox._warnings import LeakWarning
+
+        browser = utils.attach_desktop_only_warning(self.FakeBrowser())
+        for create in (browser.new_page, browser.new_context):
+            with pytest.warns(LeakWarning, match="built for desktops"):
+                assert create(is_mobile=True) == {"is_mobile": True}
+
+    def test_a_desktop_context_does_not(self):
+        import warnings
+
+        browser = utils.attach_desktop_only_warning(self.FakeBrowser())
+        with warnings.catch_warnings():
+            warnings.simplefilter("error")
+            browser.new_context(viewport={"width": 800, "height": 600}, is_mobile=False)
+            browser.new_page()