This can be reproduced on CentOS7. I tried also on Windows 10 and it works just fine. Steps to reproduce: in firefox about:config set media.navigator.enabled = true media.navigator.streams.fake = true media.navigator.permission.disabled = true Make sure you have no devices attached to the machine(microphone / camera etc.) go to https://test.webrtc.org/ Expected behavior media.navigator.permission.disabled is set to true so it should automatically start test Actual behavior It asks for permissions. But permissions are granted in this case. Note: We are using this in automated tests and the options worked just fine on firefox v.51. Since v.52 it is not working.