106 points
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You absolutely can tell what’s happening by reading the source code. They are using a listener and a delay for when ontimeupdate promise is not met, which timeouts the entire connection for 5 full seconds.
17 points
I’m sorry but I don’t see how that check is browser-specific. Is that part happening on the browser side?
30 points
They don’t need to put incriminating “if Firefox” statements in their code – the initial page request would have included the user agent and it would be trivial to serve different JavaScript based on what it said.
26 points
Easy enough to test though. Load the page with a UA changer and see if it still shows up when Firefox pretends to be Chrome
8 points
9 points
2 points