findings: (a) when it fails, the console showes `NotAllowedError: The play method is not allowed by the user agent or the platform in the current context, possibly because the user denied permission.` (b) `./mach wpt` can't reproduce. firefox-release can't reproduce. moz-regression can't reproduce Firefox nightly (or self debug build) with local served wpt can reproduce.
Bug 1524154 Comment 10 Edit History
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findings: (a) when it fails, the console showes `NotAllowedError: The play method is not allowed by the user agent or the platform in the current context, possibly because the user denied permission.` (b) `./mach wpt` can't reproduce. firefox-release can't reproduce. moz-regression can't reproduce Firefox nightly (or self debug build) with local served wpt can reproduce. And it's not clearly tangled with pref `network.http.send_window_size`