Firefox disables battery status
https://www.theguardian.com/technology/2016/nov/01/firefox-disable-battery-status-api-tracking [www.theguardian.com]
2016-11-03 06:27
At long last, Firefox has removed the privacy leaking battery API.
To arrive in FF52. https://www.fxsitecompat.com/en-CA/docs/2016/battery-status-api-has-been-removed/