Maximize what's tested on CI: a new e2e job fetches the public firefox-9 binary
and runs all 138 @pytest.mark.e2e via scripts/run_e2e.py under xvfb-run. The
wrapper launches Firefox HEADED on a (virtual) display, which is stable on the
hosted runners — unlike the true-headless drive-gate that flaked. Secret-free
(public binary + local fake-SOCKS for webrtc), so safe in public CI; the proxy
realness gate (fppro) stays local. Trial-running now; will tune if xvfb/timeouts
need it.
