Pin fission.webContentIsolationStrategy=0 (IsolateNothing) in baseline
prefs. FF150 ships strategy=1 (IsolateEverything) by default, which
site-isolates every cross-origin iframe into a separate webIsolated
content process even when fission.autostart=False - different from
FF146 Playwright behavior. The parent's Juggler FrameTree then sees
the iframe placeholder with no docShell, no URL and a stale execution
context, so content_frame() returns None, frame.evaluate() throws
cross-origin permission errors, and frame_locator(...).click() times
out. Reproduced with a local cross-origin HTTP harness (two 127.0.0.1
ports = two SOP origins).
The fix is a single pref because that's the level the original Juggler
code paths assume - vanilla Playwright Firefox 146 ran with the looser
default. Disabling site-isolation costs nothing for a single-user
puppet browser; process-per-browser/profile isolation is unaffected.
Caller can A/B per session via
extra_prefs={"fission.webContentIsolationStrategy": 1}.
Tests: tests/test_cross_origin_iframe.py adds 4 unit sentinels (pref
in baseline, survives translate_profile_to_prefs, extra_prefs override
works) and 5 e2e sentinels that spin up two local HTTP servers on
random free ports and verify the four protocol operations that
regressed (page.frames URL tracking, content_frame(), frame.evaluate(),
frame_locator(...).locator(...)) plus dispatch_event('click')
end-to-end, for plain, sandboxed and titled iframes. A future FF
upgrade or A/B flipping the pref will fail the suite before shipping.
Verified clean: pytest -m unit (342 passed), fppro_full.py (ALL
CRITICAL FLAGS CLEAN), fppro_consistency.py (visitor_id stable).
BINARY_VERSION stays firefox-7 - Python-only release.
Issue: https://github.com/feder-cr/invisible_playwright/issues/20
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
