Timezone differs between the main thread and a Web Worker
br.timezone_worker_vs_main · convicts
What it catches
Timezone realm coherence (the geo-spoof analog of worker_divergence). A residential-proxy geo-spoof patches Intl.DateTimeFormat / Date.getTimezoneOffset in the main realm to match the proxy's country, but a JS patch cannot reach Web Worker scope, so a Worker reports the REAL host timezone while the main thread reports the spoofed one. Unlike GPU/canvas, timezone is a deterministic PROCESS-level setting with no hardware variability — a real browser, and a legitimate CDP timezone override (Emulation.setTimezoneOverride, which reaches workers), report it identically in every realm — so this ships ACTIVE, not experimental. Grounded headless: real browser and CDP-override browser show no divergence in either UTC offset or IANA zone; a main-only Intl/Date spoof diverges. Fires only when the Worker reports a timezone and its offset or zone differs (missing → never fires).
Signals it reads
browser.timezone_worker_divergence
How it fires
present
Evaders it caught 2
Bypassed by 10
Frontier evaders that reach the detector uncaught (scored only suspicious, defeating every convicting tell) — this check is not one that stops them. The red-team frontier this detection still has to convict.