However it might be that the list is not always up to date with the very latest releases. That website states that it should work on Firefox v83 on Android (released on Nov 2020). In any case it is always good to design a fallback for unsupported browsers.
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FYI: The demo seems not to be working with Firefox 84.1.1 on Android 10.0.0.182 (Huawei P20Pro).
It works with Chrome on the very same phone.
Thanks for the hint. For the API support you can refer to caniuse.com/?search=Vibration
However it might be that the list is not always up to date with the very latest releases. That website states that it should work on Firefox v83 on Android (released on Nov 2020). In any case it is always good to design a fallback for unsupported browsers.